Iphone unable to send text messeges to certain numbers!?

For some reason I have not been able to text certain verizon numbers since Sunday. My girlfriend is the main person I'm having this problem with and every time I text her I get the message, "error invalid number please re-send using valid 10 digit mobile number or valid short code." She can send me texts and she can receive texts from any phone but an iphone. I say this because I have used my iphone, my brothers and also a friends iphone and all of them come back with the same message. if I use other phones it comes through just fine. I have searched and tired everything from reformatting my iphone, resetting network settings, deleting the contact info multiple times and ways, and I even had a new sim card put in. Does anyone have any ideas how to solve this problem?

jmann said:

Call AT&T and say "WTH?!". They can hopefully fix it, it might be on their end.

Click to expand...

After trying just about everything I think the problem is with Verizon. I tried another phone, a nextel from sprint I believe, and it came up with an error saying the number was a landline and couldn't receive text messages. So who knows what's going on but I'm assuming it's nothing At&T caused at this point. I'm pointing the finger at Verizon