# Why can't I have two cell phones with the same number? **URL:** \ **Category:** Factual Questions\ **Created:** [December 28, 2009, 4:05am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770 "2009-12-28T04:05:46Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![DrCube](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DrCube](https://boards.straightdope.com/u/DrCube)\ **Post date:** [December 28, 2009, 4:05am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/1 "2009-12-28T04:05:46Z")
So I bought my wife a [rotary cell phone](http://www.sparkfun.com/commerce/product_info.php?products_id=286) for Christmas, but it’s kind of a pain to remove her SIM card and put it in the rotary every time she wants to use it. It would be nice if she could have both phones ring when someone calls, so she can use whichever she’s in the mood for. Now, having multiple phone lines is no big deal with POTS service. But doing some googling, it seems the SIM cloning is extremely frowned upon, if not outright illegal. They make it very hard to do. So my question is part GQ, part GD: First, what are the details here? I’m extremely ignorant, so maybe I’m just confused. Is there really no way to get a second phone attached to a cellular number? Is it illegal, or just hard to do? Second, why? Okay, so [Wikipedia](http://en.wikipedia.org/wiki/SIM_cloning) said it makes it hard for law enforcement to track calls and whatnot. It also is used to “unlock” phones. Is that really worth making something that seems so simple and useful illegal? Why am I just now hearing about this? It was common as can be for land lines; why haven’t people been complaining about this since cell phones were invented? Anyway, in addition to the factual stuff, I’d like to debate the wisdom of this and the practice of “locking” phones. Why? Is it a good thing, or does it just line the cellular provider’s pockets? ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 4:22am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/2 "2009-12-28T04:22:00Z")
> [@DrCube](#): > > Now, having multiple phone lines is no big deal with POTS service…It was common as can be for land lines Are you really sure that having two separate physical locations (outside the in-house hardware and the network interface outside your house) for the same phone line is something that local phone companies offer? To answer your last question, there is a PR reason, and a real reason claimed reason: they subsidize your phone and thus the tradeoff is that it’s network locked real reason: they don’t want you to leave until they’ve gotten enough revenue from you. i believe the practice nowadays is to give customers the unlocking code to unlock the SIM-lock if you’re out of contract and have been with them for x number of months. ---
**Author:** ![Sal\_Ammoniac](https://avatars.discourse-cdn.com/v4/letter/s/8dc957/32.png) [@Sal\_Ammoniac](https://boards.straightdope.com/u/Sal_Ammoniac)\ **Post date:** [December 28, 2009, 4:27am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/3 "2009-12-28T04:27:54Z")
Possible workaround: apply to get a Google Voice number, and give that out as your primary phone number. Google Voice can direct your calls wherever you wish. ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 4:29am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/4 "2009-12-28T04:29:14Z")
> [@Sal\_Ammoniac](#): > > Possible workaround: apply to get a Google Voice number, and give that out as your primary phone number. Google Voice can direct your calls wherever you wish. That won’t help - there’s only one SIM card that either has to be in the cell phone or this getup that he bought (which is basically a cell phone) ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [December 28, 2009, 4:35am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/5 "2009-12-28T04:35:38Z")
There’s a technical reason why it is not allowed. Your phone constantly sends out a signal that says, “Here I am!” and the routing is stored so that if someone calls, it is routed to the nearest tower quickly. The system was not designed to have two locations for one number. You could program the phone yourself (if you know the process; I have), but the system doesn’t distinguish you by phone number, but by a unique hexadecimal code that is associated with the phone number. That hex code and the number must be inserted in the national system. So if you programmed two phones with the same phone number, only the one the system knows about by hex number will ring. There’s no reason why the system couldn’t be designed as you wish, but it wasn’t, and probably won’t be. ---
**Author:** ![Uzi](https://avatars.discourse-cdn.com/v4/letter/u/91b2a8/32.png) [@Uzi](https://boards.straightdope.com/u/Uzi)\ **Post date:** [December 28, 2009, 4:37am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/6 "2009-12-28T04:37:26Z")
When I visited Hong Kong, I took an old GSM phone from work and bought a sim card in the airport to put in it. 20 later I had the sim card and 180 minutes to use before I had to top it up at any convenience store. The cost of a call from HK to Canada was less than the cost of calling locally in Calgary on my current mobile phone. .07/min to Canada vs. $.25/min local calls in Canada. Yeah, it is expensive in Canada partly due to me now wanting to pay for a more expensive plan, but I use the phone so rarely that the higher cost per minute is better than being locked into a plan. As my phone in Canada is a CDMA phone I can’t swap out sim cards, so I’m stuck with an obsolete phone. Why can’t I just go down to a store, buy a sim card, and put into whatever phone I want like I can do easily in HK? ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 4:38am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/7 "2009-12-28T04:38:54Z")
> [@Musicat](#): > > You could program the phone yourself (if you know the process; I have), but the system doesn’t distinguish you by phone number, but by a unique hexadecimal code that is associated with the phone number. That hex code and the number must be inserted in the national system. Can’t 2 phones and SIMs be made with the same hex code? That sounds extremely problematic from a call routing standpoint (if one’s in california and one’s in NY, for example) but I don’t know enough about wireless phone stuff to know if that’s even feasible ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 4:39am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/8 "2009-12-28T04:39:54Z")
> [@Uzi](#): > > Why can’t I just go down to a store, buy a sim card, and put into whatever phone I want like I can do easily in HK? Um, you can. It’s called prepaid. It is ubiquitous in the United States and probably Canada too. ---
**Author:** ![Ruminator](https://avatars.discourse-cdn.com/v4/letter/r/b9bd4f/32.png) [@Ruminator](https://boards.straightdope.com/u/Ruminator)\ **Post date:** [December 28, 2009, 4:41am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/9 "2009-12-28T04:41:55Z")
> [@Sal\_Ammoniac](#): > > Possible workaround: apply to get a Google Voice number, and give that out as your primary phone number. Google Voice can direct your calls wherever you wish. Well, I have one of those “follow-me” type of numbers and I’ve learned that it doesn’t get around people’s tendencies to shortcut system you’ve put in place by making note of the number you call from. For example, John calls my Google #555-123-4567 which then forwards to 555-867-5309. Works great… until… I miss John’s call for whatever reason and I have to call him back. Now, John sees 555-867-5309 on his caller ID. He will make a mental note of 555-867-5309 and use that instead of the Google # for all future calls to me and Jenny. ---
**Author:** ![emacknight](https://avatars.discourse-cdn.com/v4/letter/e/3ec8ea/32.png) [@emacknight](https://boards.straightdope.com/u/emacknight)\ **Post date:** [December 28, 2009, 4:44am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/10 "2009-12-28T04:44:45Z")
Based on my expertise of having watched thousands of cop dramas, the solution is to clone your sim card. ---
**Author:** ![Uzi](https://avatars.discourse-cdn.com/v4/letter/u/91b2a8/32.png) [@Uzi](https://boards.straightdope.com/u/Uzi)\ **Post date:** [December 28, 2009, 4:47am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/11 "2009-12-28T04:47:44Z")
> [@Rumor\_Watkins](#): > > Um, you can. It’s called prepaid. It is ubiquitous in the United States and probably Canada too. You mean a long distance calling card? That is different from a sim card, isn’t it? ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 4:51am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/12 "2009-12-28T04:51:55Z")
> [@Uzi](#): > > You mean a long distance calling card? That is different from a sim card, isn’t it? No, I mean a prepaid SIM [http://www.t-mobile.com/shop/phones/Detail.aspx?class=prepaid&device=53299206-c069-429a-82fa-000007a2ac12](http://www.t-mobile.com/shop/phones/Detail.aspx?class=prepaid&device=53299206-c069-429a-82fa-000007a2ac12) [http://www.fido.ca/web/page/portal/Fido/PrepaidPlans?forwardTo=prepaidPlans](http://www.fido.ca/web/page/portal/Fido/PrepaidPlans?forwardTo=prepaidPlans) ---
**Author:** ![DrCube](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DrCube](https://boards.straightdope.com/u/DrCube)\ **Post date:** [December 28, 2009, 5:01am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/13 "2009-12-28T05:01:02Z")
> [@emacknight](#): > > Based on my expertise of having watched thousands of cop dramas, the solution is to clone your sim card. From your link: > [@](#): > > V2 or later SIM cards are very difficult to copy as additional copy protection and anti tamper protocols have been added to the cards. A V2 card is anything made circa 2002 and later (this includes 3G cards). Any attempt to copy a V2 or newer card could result in the card being rendered utterly useless. [QUOTE=Rumor\_Watkins] Are you really sure that having two separate physical locations (outside the in-house hardware and the network interface outside your house) for the same phone line is something that local phone companies offer? [/QUOTE] I’m talking about having several phones in my house ring whenever someone calls me. This way I can answer and make calls from whichever phone is more convenient. > [@](#): > > claimed reason: they subsidize your phone and thus the tradeoff is that it’s network locked > real reason: they don’t want you to leave until they’ve gotten enough revenue from you. i believe the practice nowadays is to give customers the unlocking code to unlock the SIM-lock if you’re out of contract and have been with them for x number of months. I could see that being the case if they didn’t _already_ charge draconian sums for early contract termination. So far, Musicat’s explanation is the only one that seems legitimate – and yet from what I can tell it is possible, just extremely hard and of dubious legality, to clone a SIM card and use the same number with two phones. And we’re leaning towards the pay-as-you-go SIM for her rotary phone, but it isn’t the same since it won’t have the same number. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [December 28, 2009, 5:02am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/14 "2009-12-28T05:02:49Z")
Would a cellphone docking station help? If you can find one compatible with your phone, at least you could have multiple phones in the home linked to a docked cell phone… [http://www.phonelabs.com/prd05.asp](http://www.phonelabs.com/prd05.asp) e.g. I am completely ignorant on the subject, so I won’t be of much help, I’m afraid. I’ve only heard about them the last few years and don’t know anyone who uses one. Phones are locked to make it easier for a carrier to provide you with a teaser phone which binds you to the carrier. I’ve persuaded them to unlock them before (for overseas use) and of course there are hacks which do so…probably illegally. ---
**Author:** ![emacknight](https://avatars.discourse-cdn.com/v4/letter/e/3ec8ea/32.png) [@emacknight](https://boards.straightdope.com/u/emacknight)\ **Post date:** [December 28, 2009, 5:06am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/15 "2009-12-28T05:06:36Z")
> [@DrCube](#): > > From your link: > > I’m talking about having several phones in my house ring whenever someone calls me. This way I can answer and make calls from whichever phone is more convenient. > I could see that being the case if they didn’t _already_ charge draconian sums for early contract termination. > > So far, Musicat’s explanation is the only one that seems legitimate – and yet from what I can tell it is possible, just extremely hard and of dubious legality, to clone a SIM card and use the same number with two phones. If they’re all in the same house than they’re all using the same tower, so no big deal. At the end of the day, this is done by a variety of tv-based law enforcement entities to eavesdrop on a cellphone call. ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 5:08am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/16 "2009-12-28T05:08:17Z")
> [@DrCube](#): > > From your link: > > I’m talking about having several phones in my house ring whenever someone calls me. This way I can answer and make calls from whichever phone is more convenient. The only proper analogy for a cell phone is if you have your own cell phone tower in your house that is permanently and exclusively locked to your cell phone and subscriber account. This is like asking why can’t trains travel on the NY thruway. ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 5:09am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/17 "2009-12-28T05:09:19Z")
> [@emacknight](#): > > If they’re all in the same house than they’re all using the same tower, so no big deal. I could see this being true for the boonies. But a densely populated area? ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [December 28, 2009, 5:15am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/18 "2009-12-28T05:15:13Z")
Missed edit window: that thing that Chief Pedant linked to is a less inane analogy:D ---
**Author:** ![DrCube](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DrCube](https://boards.straightdope.com/u/DrCube)\ **Post date:** [December 28, 2009, 5:15am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/19 "2009-12-28T05:15:21Z")
> [@Rumor\_Watkins](#): > > The only proper analogy for a cell phone is if you have your own cell phone tower in your house that is permanently and exclusively locked to your cell phone and subscriber account. > > This is like asking why can’t trains travel on the NY thruway. Right, I understand that cellular networks are physically and conceptually different from POTS networks. And if it wasn’t possible, I’d take Musicat’s answer as the final word and be done with it. But some googling make it seem that there are people out there who, through much effort and with questionable legality, manage to clone their SIM and use multiple cell phones with a single number. Is it just a matter of “A few hackers can get away with it, but if we allowed everyone to do it we would have to redesign the entire network”? ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [December 28, 2009, 5:20am UTC](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770/20 "2009-12-28T05:20:35Z")
The phone system must know the ESN (Electronic Serial Number in Hex) for the phone. It associates it with the number people dial to reach the ESN. When you sign up for a phone account, this number pair is entered into the national system. When someone phones your number, the last known location of the corresponding ESN is used to route the call. So it is possible to have many phones with the same phone number but a different ESN, if you program it yourself (cloning is one way), but when you try to tell the system what your ESN is, it will replace any other set of ESN/phone numbers, wiping those out. Or, if you don’t tell the phone system about it, it will never ring. Making emergency calls from the phone will probably work, cause there is no verification of ESN to let the call thru. But…somewhere along the line, things are going to be confused, you betcha. [Next page](https://boards.straightdope.com/t/why-cant-i-have-two-cell-phones-with-the-same-number/522770.md?page=2)