Will all phones work on any network now if you get the right sim card or do individual networks still have exclusives on phones so you have to purchase their model?

It is my understanding that you have to buy an unlocked phone and then obtain a SIM card from your choice of wireless service provider.

I do not know if you can buy a phone from AT&T for example and then put a SIM card from Verizon in it and use it on the Verizon system.

The wireless companies put extra apps on the phones they sell in hopes you will use their apps giving them sellable data. If you bought a phone from AT&T for example and then wanted to use it on Verizon for example, Verizon would not reap any benefit other than your monthly fees.

They still sell phones locked to one carrier. If you buy a phone on contract, they will unlock it for you after the contract term is over.

I got off the contract treadmill years ago by buying phones on eBay. The last two were an LG Nexus 5 (Nexus phones are always unlocked) for $189 and a Moto X 2013 for $75 (plus $20 to get an unlock code from a third party).

The Nexus was new, the Moto X looked like new.

If you’re shopping for a good wireless service provider, I can recommend Project Fi. (I would link it, but when I pull up the website, it gives me my account information.) It is Google’s wireless service, and only works with Nexus and Pixel phones. I bought the Pixel XL when it was introduced last fall, and I love it. I highly recommend it. However, this works best for individuals who use Google products like Gmail, Maps, etc. This phone knows what I’m going to do before I know.

Nope. Certain carriers use different communication and radio architectures. GSM and CDMA are the main two. This is why you can’t simply unlock a verizon phone and use it on AT&T. Some phones have both sets of architectures and some don’t.

IT is both the radio architecture and the radio frequency the carriers use, they are not all using the same bands. Some carriers paid big bucks for exclusive radio frequencies.