I just did this for a full 30 days in January and February to test out AT&T service in my area. Everything worked well after doing the APN changes mentioned by dpham00. When I received my SIM card kit from Straight Talk I followed the directions and everything worked great. There is no LTE, but I was getting 4-8 Mb/s on HSPA+ on AT&T. Plenty fast enough for my use. Now I know that I can use either AT&T or most likely one of their MVNOs when my contract is up with Verizon.