Motorola Q won't send text messages

I have a Motorola Q on the Alltel network. I am using the AlltelU pay as you go plan-I know, the Q is supposed to only be used with a data plan. I got the Q activated over the phone after they would not do it in the store. I did not tell the rep what type of phone it was. Afterwards, everything worked great including sending/receiving text messages!!

So, after a month, I call in to switch to a $5.00 text package instead of paying 15 cents per text received/sent. After doing so, phone worked fine, but I no longer could send or receive text messages. I call in to customer service--rep asks what type of phone and after she finds out I am using a Q on a pay as u go plan, she deactivates it!!!!

Well, I call back in and re-activate the phone with no problem. Thinking I am good to go, BUT, I can receive text messages, but I get an error message when I try to send them. I did a complete reset of the phone and the problem is still present. Is it a problem with the phone, do I need to change a setting, or is it my pay as you go plan??? Any help is appreciated!