One final possibility: try starting the phone in Safe Mode and see if that solves your problem. If so, it might be an app you installed at around the same time as your switch which is causing the problem.
Additional possibility, though it may seem dumb: make sure you are not accidentally covering the mic with your small finger when you are holding the phone. It happens. Seems unlikely in your case as you didn't have a problem before.
Have you tried a friend's SIM (from another network) in your phone? This would at least help confirm that it's not a hardware/software problem of your phone. Seems unlikely given that you tried the SIM on another phone.Also have you tried the SIM in ...
Not sure whether an American credit card will work...just checking up on that now. But defintely the address information has to match the credit card in order to work. That's one of the ways they verify it online.
