It makes me think of "cordless phones" in a house (assuming people still have land-lines LOL) ... you don't need a specific cordless phone depending on who your telephone provider is. You just buy the phone you like, plug it into the phone line, and you're in business.
It's a crying shame that cellular network service is as chopped up and segregated as it is, that phones have to be made for each carrier.
A cordless phone is analog - and analog voice is analog voice. s long as the phone can handle about 300-3,000Hz, it can handle everyone's voice.
Cellphones are digital, and there are about 15 different ways to digitize an analog signal (like a voice), and different companies were allied with different chip or technology companies, so we now have 2 totally different cellphone technologies. (You don't need a different phone for each carrier, any unlocked GSM phone that has the right frequency radios will work with any GSM carrier.)
Remember history, though. At one time you couldn't buy whatever phone you wanted - the Bell System gave you a phone and charged you for it every month - for decades. Even if you had your own phone (and it would be an RCA or Stromberg Carlson - Bell instruments weren't for sale), connecting it to Bell's network could get your account closed.
Once the Bell breakup occurred, they weren't about to throw out 75 years of reserch and development and come up with incompatible systems. Burning their money would have been cheaper and easier.
Cellphones? Once the system went digital (back in MTS and IMTS days, anyone could convert any two way radio into a mobile phone and register it), some places went with CDMA, some with GSM (and I'm surprised we don't have P25 systems and a few others - they could
really drive us nuts if they wanted to). It was a new technology, so they were free to innovate without throwing out existing systems.
I'm just talking about which type of antenna are in the phone ... how many antenna are in the phone ... which "bands" or "channels" they are set up to use ... which features are enabled/disabled ... so on and so forth.
You can't use the same antenna for GPS, wifi, 700MHz, 2600MHz, etc. unless someone reinvents physics. A quarter wave at different frequencies is different lengths, and there's no simple way to make one antenna cover all the frequencies used, and all the sensitivities needed (GPS signals are
much weaker than cellphone signals), without the antenna costing a
lot more than 4 or 5 separate antennas.
I'm sure there's way more about how all this works than I will ever know ... but man, it's a shame that it's not all just one huge network, and you just go buy a phone - whichever phone you prefer, and plug in your sim card from your preferred carrier - and rock on. It just doesn't seem like you should have to wonder how your version of a phone is going to come equipped ... or when your software will get updated, ... Just give me my phone, and let me use it. I will pay for the network service, and for the data as my carrier says I will (and that I agreed to when I chose said carrier) ... and that's that.
Well ... for the reason it's not that way - and can't be that way - read the first sentence in your above paragraph. They'd close my account for making a long enough post for you to understand it all - or even to understand what the industry went through from the 60s to the turn of the century. But back when anyone could use any "mobile phone" on any carrier (and that was Bell, except for a few small places way out in the boonies - like Marked Tree Arkansas - loads of people in New York City had phones registered there, because all the NYC numbers were used up), in order to make a call, you could get laryngitis yelling "mobile operator" until you got her to stop yapping with the operator next to her and answer you. IMTS (dialing your own calls) seemed like science fiction. But there were still only 24 channels for any given area - so in just about all of a large city, you couldn't have more than 24 calls being handled at once. (Which was okay - a phone cost about as much as a Chevy, a call was about $1.50/minute - when people thought $10,000/yer was pie in the sky, so not many people were making mobile calls at one time. IMTS increased that to 35 channels, but can you imagine a place like St. Louis being limited to 35 mobile calls at a time?)
Now, even though there may be some problems - your CDMA phone won't work on a GSM carrier, CDMA carrirs won't activate another CDMA carrier's phone, etc., if you want to spend the money, you just dial a number in China and it takes as long to get connected as it takes to get connected to the person standing next to you. And the call quality is just as good. (And the phone fits in your shirt pocket, not in your car trunk.)
I'll take it the way it is now, if the alternative is MTS - or even IMTS.