If you are unable to SEND an SMS Text Message and they get stuck in Unsent Messages:
Messages, Menu, Settings, Call Back Number. Your Call back number can NOT contain dashes or any other symbols. If you put in, for example 212-555-1212 it will break outgoing SMS Text Messaging. Remove the dashes to fix!
If that doesn't work, you can also just reset the SMS Settings: Open Messages app, click on Menu, select Settings, click on Menu again, and finally select "Restore Default Settings" This will restore the default SMS / MMS settings only.