Driving me nuts!

[rabernet]

I'm trying to send a text to a friend of mine - to his cell, but I keep getting a message "xxx-xxx-xxxx is a landline #. Reply Y to send all TXT messages to this # as voice messages for $0.25/msg + std msg fee. Details @ vtext.com, TexttoLandline"

I KNOW that this is not a landline, I've texted him many times before from my previous phone. Any work around?