Can I put my T-mobile sim card into an AT&T phone?

I wanted to get a new phone but I liked a phone from AT&T. Should I get it even though I have a T-Mobile plan?

i no until you unlock your phone from AT&T network you can't use it with t-mobile sim ..You can easily unlock your phone using sites like Classicunlocking.com here they render unlock code for all mobile models at reliable cost ..You first verify that whether they are rendering code for your mobile model ..If yes then pay for it and unlock your phone ..