This is a problem I've had over a year ago and don't think it's ever happened again until now. The fix I had to do back then was to webdoctor. Since then there have been some new updates and I even got a new Pre and haven't had the problem (as far as I know) until today.

I have a Sprint Pre- running webOS 1.4.5
Here are the some previous threads about this issue:

This time I didn't have the contact saved, just the phone number I've called and had called me back. But when I press the SMS button from the dialer, nothing happens. When I have the messaging app to type in that number directly to text, nothing happens either. Again it only happens to one specific number, everyone else I text works as normal. Since it's not a saved number, I know it can't be a problem with Google or Facebook contact/profile syncing.

This is the ONLY software bug/problem in which I've EVER had to use webOS Doctor before... over a year ago. And I'm really hoping I DO NOT have to do a wipe and fresh install just to fix this stupid (but apparently extremely rare) bug that only a handful of us have had the misfortune to experience.

I'm also REALLY hoping that this bug doesn't exist at all in any of the newer webOS devices like the Veer and upcoming Pre3. Although I'm still stuck with the crappy choice between staying with Sprint or sticking with webOS...