I would prefer to dial 11 digits for every single telephone number within the ###-###-#### system, even across the street. It removes the burden of having to know when you need extra digits, it simplifies programming devices that call automatically, and local numbers follow a small number of patterns anyway.
As Sunspace said, we tried that in NYC with 917. Afterwards, the FCC slapped everybody’s hands and said, “No technology-specific overlays. They’re anti-competitive.” They grandfathered 917, though.
Unfortunately, 212 exhausted before a relief plan was in place, so 917 had to be opened to business landline customers, thereby screwing up a good thing.
You know - the “Boy, we could have done a better job on that” thing.
We split in NV, and that seemed to work okay. I guess I really don’t care.
I’ve lived in Los Angeles my entire life. The area encompassing LA, San Bernardino, Riverside, Orange and Ventura Counties, often called Greater Los Angeles, used to be just four area codes – 213, 714, 805 and 818. In just 17 years, those same areas have grown to have 213, 310 (1991), 323 (1998), 424 (2006), 562 (1997), 626 (1997), 661 (1999), 714, 760 (1997), 805, 818, 909 (1992), 949 (1998), and 951 (2004), with 647 coming sometime this year. Splits and overlays aplenty.
So yeah, I don’t really care anymore. But I think overlays make the most sense.
If you always dial the 1, it’s meaningless. The system might as well drop it, and just let you dial ten digits, starting with the area code.
The problem is that the NANP has a confusing array of intra-NANP dialling plans. In some areas, you dial a 1 before an area code, whether it’s local or not. In others, you dial a 1 before a long-distance call, whether it’s in the same area code or not. Some of the second type of area, such as Ontario, do not allow you to dial a 1 before a local call.
This is what we have to do in Orlando(ish). It was a bit of a problem during the switch, since suddenly I couldn’t call my kids’ daycare because my employer hadn’t updated the phone software, but it was quickly handled.
I’m so used to it know I don’t even think about it. Besides, my family lives in other area codes, so I have to dial the full 10 digits anyway.
Wow. That’s gotta take the NANP record for “most area codes in a metropolitan area”.
Nitpick: 647 is already in use in Toronto (my cellphone uses it). So unless you want to give 2.5 million Torontonians free calling to L.A., it’s probably something else. 
New Mexico just split in October, and I would have preferred an overlay. With a split, I had to reprogram my cell phone for about a third of my phonebook. In addition, I had to change my number.
Strike that, I would have very strongly preferred an overlay, because now my area code is different than everybody else’s, because I still have my cell phone number from college.
And that’s why I hate both overlays and splits. When my father was living in the Chicago suburbs, he had four area codes in the space of 8 years, which sucked.
OTOH, I’m right on the dividing line between the original area code and the split, so to dial some place a mile away, I have to dial 10 numbers. But to call another place in that same area code, I have to dial 1+ 10 numbers. And if I get confused, there’s always a helpful SCREE-EE-OOO to remind me I dialed wrong.
Oops…I’ve apparently given away the secret plans for the Los Angeles invasion of Toronto later this year. :smack:
Either that, or I meant to type 657. 
I’ve been through both, and overlay is, to my mind, the only real option.
Unlike the 1/no-1 thing with long distance calling, 10 digit phone numbers work regardless of whether they’re necessary. You may not need the area code for your local call if you’re in a non-overlay area, but dialing it won’t cause the call to fail. So anyone who has automated dialers or computer programs that need to call specific numbers should already have them programmed for 10 digit dialing.
Then, an overlay can be done with 0 impact to anything, basically. New lines get numbers in the new code and life goes on. And, more importantly, it can be done with the same no impact repeatedly. Split and need a third code? Massive upheaval once again. Overlay and need a third area code. Presto, third area code.
Splitting, on the other hand, causes a massive number of people to have to get new numbers. To make sure that everyone they deal with, friends, businesses, etc, know they have a new number. It causes businesses to have to reprint metric buttloads of stationery, forms and business cards (which is, of course, totally environmentally friendly).
Splitting also has an odd side effect in that many businesses end up wanting the same number in both area codes so that customers on both sides of the split can continue to make the same call and reach them. All of which artificially increases the demand for new numbers thus ensuring everyone will have to go through this all again sooner than they otherwise would have.
7 digit dialing was a matter of great convenience back when we had rotary phones and dialing a phone was a pain in the ass. We’re well past that point now.