Will an unlocked iPhone 4 work on Tmobile now?

I don't really have the money to dish out on an iPhone 5 on the Tmobile network, even though I already have a Galaxy S2, with them. I was wondering if I could buy an iPhone 4/4s from amazon, and just get a sim card for it, since they are an offical iphone carrier now?

People have been using unlocked iphones on tmobile for years

Only problem is they get 2g edgr internet (basically unusable )