I got my son the LG Ally when he went off to college last year. Unlimited texting plan is in place. I have been able to send him texts from my computers using Windows Live Messenger for the last year. Now, within the last week I cannot send him text messages this way. I get a return error that says "This message was not sent because messages can't be sent to this mobile number."
Nothing that I know of has changed with the phone, the service plan or with Windows Live Messenger.
Any ideas what is going on?