I know this is late for the OP, but it will help others down the road.
try a programming refresh.
The LG Motion is CDMA so this SHOULD work you.
Go into the phone dialer and press ##626*, a box should pop up asking you for a service code, type in 587846.
One you do this, a small menu should pop up. Now I no longer have the Motion so this is a little fuzzy. I believe what you want is NAM Programming. Once you click into that, you'll see 3 fields of numbers. Just click edit, and ok on each one as if you were editing them but don't change anything. Once you press edit and ok on each one, press done. Your phone should now turn off and reboot. Try to send a text now...
This WILL NOT delete any user data at all, this will simply do a complete network reset / refresh, and 99% of the time solves all text messages issues. At least it did for me and everyone I would do it for.
Give it a try, and get back to us.