Probably next to impossible, but could it be done? I always like the old Motorola StarTac phones-could you simply put a new mother board inside the thing?
Sure.
Not within a reasonable cost range, no. If you had mad tech and engineering skillz and lots of time you might be able to gut a small, basic CDMA phone and wire up the circuit board to the old keys, lights and antenna, but it would be a huge kludge that accomplishes nothing useful other than saying it can be done.
So … no.
Antennas of that era tended to have less sensitivity than modern ones do. You’d have to make sure you have useful ones.
If you’re going to design the insides from scratch, you’d also have to fight space requirements, but modern chipsets tend to be smaller than the old ones, so you’re probably ok there.
Then you need to come up with software to run on your new phone.
-D/a
They are so different (there’s really nothing the same about the two) that about the only way would be to make an old style ‘shell’ whose buttons just pushed corresponding buttons on a modern one slid inside it. Even that would be difficult.
This site sells old, supposedly working and still usable cellphones, but only the original ‘brick’ style ones.
It’s quite possible and I’ve thought about doing it for years with a cheapie prepaid phone, I’ve got the skills but I’m lazy and haven’t wanted to spend my money that way. If you can wire up a joystick it’s pretty much the same thing. I haven’t seen a brick phone in good cosmetic condition in a while locally, they used to be at Goodwill all the time, wish I had picked one up.
Wiring the keys up is similar to wiring a joystick.
Wiring the antenna is very different. The RF world is much pickier about wiring than the digital world.
Still doable. But you might get crappy reception if you don’t do it right. 
-D/a
Are CDMA and TDMA technology even used anymore? Even if the OP was able to convert his old Startac from analog to CDMA it may not work on a modern network.
Motorola Startacs were made in digital versions (I had a CDMA model dating to 2000) so it’s possible for the OP to obtain one (probably for rather cheap) and not having to bother converting his old phone.
Verizon and Sprint are both CDMA carriers; as well CDMA is still common in parts of Asia.
TDMA eventually evolved into GSM.
I see.
I have AT&T and have a GSM phone so that’s why I wondered about CDMA still being used.
To follow up on that, I have a cell phone in my kitchen right now camped on Verizon CDMA 1X.
-D/a
I know absolutely nothing about antennas, I can’t just wire the new phone to the old brick’s antenna and have it work? Would the build in antenna work okay through the brick’s plastic box? It’s probably more complicated than that. 
edit: If Verizon and Sprint are still CDMA, can you call them and have them hook up your Brick phone and use it in 2012?
You may or may not be able to make a call if you just randomly wire the antenna up. There are complicated calculations to get proper ‘match networks’ based on resistors on the PCB. These effectively ‘tune’ the sensitivity of antennas. More than “maybe” becomes a fairly complicated answer.
Yes - I’d expect if you had a really old CDMA device, you could probably convince Verizon or Sprint to activate it. They might laugh. They might refuse because it doesn’t meet current standards, though.
-D/a
They should refuse, because it wouldn’t be an FCC approved device. Testing for FCC approval includes the case, antenna, etc. Changing those out would void the approval, and would be against FCC regulations to operate. Not saying the feds are going to kick in your door over it, nor that anything truly bad is likely to happen. But I’d be very surprised if the carrier would activate such a thing.
No, I was asking if a brick CDMA phone could get Verizon or Sprint service if I call them and ask them to, that is seperate from putting the PCB from a cheap prepaid phone into the brick with an already activated Sim using the Brickphone as a glorified case-mod.
I don’t think the issue is approval, the more modern CDMA devices and the networks they operate on are digital the older ones are analog. They cannot operate on the modern networks.
See
http://www.techrepublic.com/blog/wireless/analog-cell-phone-networks-are-going-goinggone/171