I have the same problem but only texting to 1 number! I have found that if I reply to a text message (if there is allready conversation history) it will not send and I get a failure report. If I delete all history from the number, it will then go through. I tried deleting the contact, but even if the contact is deleted i still have the problem! I have not contacted 3 about this yet.. but they are quite useless so I will start posting in the forums!