NEED HELP. I posted elsewhere to get no responses, so I dont think anyone read it. I need help ASAP so please accept my appologies in advance. I know you guys know your stuff and can help a hacker since the iPhone came out. Thanks.

Hey all. I have a 1st Gen iphone unlocked on T-Mobile USA> Unfortunately, I moved to a new place and T-Mobile's signal constantly jumps all over the place. Its not constant and I frequently loose service. This isn't acceptable with my job so I need a more reliable network in my area. I am very sad to let T-Mobile go, as i have loved being a customer since 2003, love my iPhone, and their prices. My fiance is on AT&T and has no problems at all here so I figure I should switch and keep my unlocked iPhone.
On to the real business. Since I will sign a new contract and be on an iPhone with EDGE, when I sign up I need to buy a phone that's plan will be compatible so when I use my iphone it works on the same service. I had heard last year that Blackberries used the correct EDGE plans for me to use an unlocked i[hone on. Is this still the case? Are there specific models I have to go with? Or can I get any phone and just add EDGE service to get the iphone going? Do I need to worry that AT&T will see that once I switch my SIM that I am on an iphone but not on iphone pricing plans? Any advice is greatly appreciated. I hope to buy my new service and phone in the next 24-48 hours. Obviously the phone that I select with AT&T will not be used, but sold most likely. I love the iphone. Thanks in advance.