I texted my wife a few hours ago and got a "message not sent" error. I tapped the exclamation mark next to the unsent message and it tried again, but failed. Amused by the possibility that it might be a confirmation handshake problem, and that she might be actually receiving them, I hit the exclamation mark a few more times. About ten.
Then, to see if it was a problem with Virgin, I tried texting my son and that one failed too. I was standing right next to him so I rang him and the call was connected. When I tried a second time the text was delivered to him, so I hit the exclamation mark next to the failed message to my wife and it sent immediately. She replied immediately, and only got the message once.