Default Galaxy Express i437 on another network?

I'll skip all the details but I bought a very nice, very expensive phone from china that ended up only connecting at edge speeds. It supported the correct frequencies but they were swapped, its data freq was voice on my carrier and vice versa. I switched carriers 3x to no avail. In desperation I just ran to walmart and bought a Galaxy Express i437 then sent the Chinese phone back at a loss.

Well, big mistake. The phones great, it suits my needs though it was a bit expensive. But AT&Ts network is complete **** where I live. I can't receive calls in my own house! I've it flashed with the latest version of Cyanogen... which actually helped my signal... but its still not enougn..

1. Can I switch to another carrier? Sprint seems to have a good network here according to the maps and people I've talked to.
2. Where can I find info on frequencies. I'm a pretty technical guy but I am baffled by these frequencies. I don't want to get stranded with no phone for another week and I dont want to blow another $300 on a phone that may or may not work!
3. Do I need to do anything to "jailbreak" my phone? Or does jailbreak just mean root? I'm suprised how little info I could find on the subject.

Yes, I do realize that I'll probably just get flamed with links to FAQs, but that's what I'm looking for! If someone just knows the answers to my questions, that'd be great to.