"Error Sending" SMS Messages on the iPhone

A number of users have reported a sudden inability to send SMS text messages on the iPhone 3G, receiving the message "error sending" upon attempting to send. Among the user reports:

• "When I try to send an SMS and i press "send", the iPhone returns "Error Sending Message". I've tried with another SIM card from another Italian operator (I use Vodafone), but the problem is the same."
• "I had the people at the store swap SIM cards with another iPhone they had there, and I they could send SMSes from their phone with my SIM card, however on my phone with their card, they couldn't send an SMS. I already restored my iPhone 3G (2.2), and still am having this problem."
• "I have this problem, as well. Interestingly, mine started 12/7, all of a sudden. I notice that several people had the problem develop that week. I spent 2.5 hours on the phone with Apple and AT&T last night. Reset everything, no one could find a solution. "

Despite the aforementioned reports, a number of users have been able to resolve this issue through SIM card replacement. Other fixes, including resets and restores have proven ineffective.