Need advice on my 4 month stay in US.

Hey guys,
I figure you guys would know best on what to do.
I am moving (from Canada to the US) for 4 months in May. I am currently with Rogers on contract here. I told them to put a hold on the contract for those 4 months. I also have iPhone 3g unlocked.
Now What I want to do is have a phone that has some txt about 200 minutes and some kind of data. I have read so many different things though saying I can get all of that for 10 a month...??

If anyone here could help me out that would be great (keeping in mind I more than likely have to stick with T mobile or AT&T) because i need the sim card.

Any links also or ebay auctions or whatever would be fantastic.

Thanks a lot guys,