I keep getting an error message when I send a text..

[DUNN28]

All the sudden today, out of the blue, my texts started failing and I keep getting the following message in the form of a text:

1(then the number) Error Invalid Number. Please re-send using a valid 10 digit mobile number or valid short code. (followed by the message I'm trying to send)

I'm using the IPhone 3G with the 3.0 software. I have tried several people and I don't even have a 1 saved with the numbers. Any suggestions?
Thanks

 

[chobbs1]

first i would do a soft reset. hold down the power button until the on/off slider shows up>>then continue holding down the power button along with the home button until the Apple log shows up. then try and send a text.

Currently in settings>>phone>>international assist I have it set to on I don't know if this would help you situation but you could try switching it on and see if that helps.

if all else fail you can either call apple or AT&T and have them assist you and as a last ditch effort you can do a restore.