I know for a fact that if I am on a phone call and my friend sends me a iMessage it just gets sent as a text and I get it.Prioritizing 3G over wifi would explain the issue I had yesterday when texting my wife. I am on AT&T and she is on Verizon (company phone). She was talking on the phone at the time and I tried to send her 3 texts (iMessage), all timed out. Verizon not doing data and voice at the same time over 3G might have been the issue. She has wifi available at her office, but she thought she was having issues with that connection. Perhaps she wasn't and it was prioritizing 3G over the wifi.