My trouble is relatively straightforward. I have an iPad 2 64gig wifi only. iMessage seems to work just fine when I'm connected to a wifi signal. Any signal. The problem seems to occur when I'm tethered to my iPhone 3GS hotspot via Bluetooth. In this mode I can browse on safari, use any of my apps that require an Internet connection and send and receive email. What I cannot do is use iMessage. It will let you press the "send" tab, but eventually I get a red exclamation mark and the "Not Delivered" message under the text. I should point out that the problem started when I upgraded to 6.0, and today's 6.1 update did not fix the problem. I've been living with the problem for a while now, but it's getting really old now. I use AT&T as a carrier if that makes any difference. Please help.