Using an SMS aggregator such as CellTrust, you could send the user a code through a shared short code. Or, if you're willing to put up with short ads at the bottom of messages, you could try TextMarks.
Looks like textmarks requires the person to subscribe before you can send messages to them: "To keep everybody happy and prevent abuse, you can only send texts to subscribers of your TextMark."
Comments
Using an SMS aggregator such as CellTrust, you could send the user a code through a shared short code. Or, if you're willing to put up with short ads at the bottom of messages, you could try TextMarks.
Looks like textmarks requires the person to subscribe before you can send messages to them: "To keep everybody happy and prevent abuse, you can only send texts to subscribers of your TextMark."
http://www.textmarks.com/dev/docs/send/?ref=devsb