can't receive pics from 8310(at&t)

i just bought the 8330 (VZW) and i've been trying to send pics and ringtones to my sister who has a 8310 (AT&T) and she never gets them. she can't send them to me either. i've been to two VZW one AT&T stores and to have them troubleshoot the problem. i'm just getting the same comment from everyone.."that's strange". i can get and send pics and rigntones from other VZW people and she can get and send to other AT&T people we just can't send them to each other. i'm considering switching to AT&T due to this and other issues but i wanted to see if anyone has suggestions....i'm at a loss right now. i just read about the different OS and don't know if that's a factor..seems like it shouldn't be. :confused: