IPhone – Unlocked iPhone replacement

So in the end I had to do the SIM card dance.

In fact, it seems what the carrier does is mark your phone as allowed for unlock.

Then, the first time you put a SIM card from another carrier, you must connect to iTunes, which will then perform a series of annoyances and alerts and whatnot, and only then your device will be truly unlocked. You need an internet connection for this process.

I know this is a terrible answer to my own question.

Will the iphone get 4g speeds

No it won't. iPhones, even 4 and 4S, are not 4G devices. The 4 is for the iPhone fourth generation, but they are in reality 3G devices. So you won't get better speed than 3G (for sure).

I'm not sure for the network itself since I'm in Canada and I don't look at US providers very often. From memory T-Mobile has a different (AWS) network than AT&T so that could also affect your connectivity and speed. You better check the phone versus provider specifications (or someone else doing the same as you).