The AT&T promotion is different from the Verizon Wireless one. The bill credits take 30 months to be fully paid out instead of 24 months with VZW. You qualify for the AT&T promotion because you are starting a new account there. There aren't two year contracts. They are device payment agreements.
Go ahead and switch if you want, but be sure to truly understand the terms of the promotion before agreeing to it.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.