Hey iphone unlocking

[MessiahJuni]

I was wondering my brother has a iPhone 4s that's for sprint but he wants to unlock it for AT&T how can I do that ?

 

[XamDam]

There is no unlock for any newer baseband at this time.
There is also no hardware unlock for newer basebands at this time.

Also note: There is only certain basebands that can be unlock and there
very limited to only around 6 basebands.