iPhone SMS Messaging Error: "Requires 10-digit number"

Recently we reported on errors iPhone users receive when attempting to send SMS messages. Users experiencing this problem might also receive errors claiming the number used is invalid, and asks for a new number.

This problem has affected users off and on for some time, and seems to be a result of an improperly formatted number synchronized to the phone. When users synchronize their phones from various computers, if their personal contact vCard includes only a 7-digit number then it will sync to the phone and cause this problem. As such, users should be sure to enter a full 10-digit number into their contact information. In addition, users should be sure to remove all text messages made with the phone prior to updating the number.

Fixes

Update personal number to include "1" and area code Go to the iPhone's contacts and update the personal information to have a phone number with "1", the area code, the 7-digit main number. In addition, update all contacts which might be synchronized with the phone. These may include Outlook address books (Windows) or "Address Book" contacts (Mac). MobileMe users should also update the contacts via the web interfaces to ensure those are not pushed back to the phone with improper information.

Remove existing text messages In the phone, tap the "Messages" option and in the list of text conversations remove any that were made before updating the phone's contacts. These old messages will still associate the old 7-digit number with the contact, and may prevent the phone from properly using the 10-digit number.