I have heard people get told both, in the end I believe it is an issue of various levels of knowledge and experience on the AT&T CS side.
Originally Posted by Sylo
SII is a "4G" phone though, so your original SIM should have been setup for "4G". I didn't have to call ATT either going from Veer (SIM shipped with Veers) to Pre3.
Originally Posted by wellwellwell11
As was said above, if you have any issues, and ATT store should swap the SIM out. I have heard of at least 1 or 2 people doing that after getting nowhere with phone CS. It wasn't worth the hassle when the SIM swap cost nothing.