Have a ATT and a Verizon (wife att me verizon). Differences are Skype integrated into Verizon not so ATT. Verizon has 3g data in the US on CDMA. Att is 4g but the Verizon phone holds signal better. Battery life better on Att marginally. Have used Verizon in europe and it works as advertised and every bit as well as my old blackberry switching from cdma to gsm. No issues. All in all I like the verizon better but the att is very nice also.
Skype is a free download for the gsm pre3 in the app catalog now, fyi.