Good afternoon! Aside from the messaging concern, I hope you are enjoying your new HTC Trophy! I know I can help get this working properly. Are you having trouble with an error message or the functionality of sending a text message? It is far different from our basic LG devices. You can find the steps to send a message in the user manual on page 51.
If there is an error message, we have more probing to do! Are you sending to an 11-digit mobile number? If not, you'll want to edit the mobile number under the contacts, delete the entire text thread, and try to send a new message. Is this affecting all people you text? Or maybe just a few specific contacts? I do recommend the standard battery pull because it works very well with these kind of concerns. Just remove the battery from the device while powered on for 10-20 seconds, then put the battery back in and reboot.
Please advise more information so I and the community can continue to assist!