Add text message (SMS) capabilities

Hi, I would like to add SMS capabilities to my site. I want users to be able to send comments from their mobile phone to a number and have those comments entered into my database as if they were sent directly from my website in a normal form submitting manner. What I need: - User's to be able to add their mobile phone number (and carrier I'd imagine) to their user info in my database (I have this code in php, but it could use some cleaning up I'm sure) - To set up a specific phone number so that people can text their comments to that number (US only for now) - Create code to recognize if the user sending a text to the above mentioned number has in fact registered their mobile info with my site. * if the user's mobile info is recognized, then proceed with a successful post * if not, then do not submit the info to the db - Also, need it to be as secure as possible so people cannot take advantage and send junk through to my site. Best offer and experience is what I'm looking for... preferably proof that you've done a similar project. Thank you, Brad