I'm having trouble using iMessage on iphone 4. I have both my iphone and ipad configured with the same e-mail address and it's working perfectly on the ipad. However, I neither receive nor send from the iphone. Whenever I compose an iMessage it starts to send but doesn't complete and send an error that the message is not delivered. The iphone is working with both 3G and wifi and all other apps that require internet access are working. Any ideas?