Can I use a T-Mobile iPhone 5 on att?

Is it possible if i had a t mobile iphone 5 if i could unlock it and use it on att or use it on straighttalk with a att compatible sim ( i'm using in my att iphone 4) if i cut the sim down and do whatever of course. So basically what i'm asking is cani use a t mobile iphone, unlock the imei and use it on att, straightalk, etc.

I believe you can do that, I did that once to one of my Iphones. If you are trying to unlock your cell phone, never do that with AT&T as there are many other unlocking companies out there that do the exact same thing, but off course cheaper than AT&T. I sometimes use http://www.cellsunlock.com to unlock my phones, they are faster and cost less than others but its up to you.