3G At&T sim card in a 4G phone

[funflea]

I just read that an At&T 3G sim card will not work with a 2G phone. Will the 3G sim card work in a 4G phone? And, if I buy a new 4G sim card does that card required activation? Can they transfer my old number as well? Thanks !

 

[hang-the-9]

Best place to check would be with AT&T. If you get a new card, it should not cost anything going from a 3G to a 4G phone and they can move your number over.