I'm with AT&T and both my iPhone4 and iPhone4S are running fine. When I go camping or go on vacation I like to take the iPhone4 and upon my return, pop the sim out and place it in the 4S for everyday use. (Different apps on each iPhone for various purposes. One is more work related than the other...) Does AT&T allow this or will I potentially get an email instructing me not to do so (for whatever reason, who knows.)?