Cannot respond to Text messages...
 

The Carrier is Vodaphone, the user is in Australia on an 8700 device. She can recieve text messages but cannot respond. Seems that it would be a carrier issue, but she says the carrier has activated the text feature for her account. Could this be a device issue somehow?

That would depend. What is the actual issue? When you say she can not respond does that mean she does not have a reply menu option? Or that she gets an error when she tries to send SMS? Or that she sends it but you never get it? etc. etc.