Text Messaging Service

I have a client that wants to put a form on their site for a user to enter a cell phone # and then be signed up to receive text messages from this business. Does anyone have any good references of online services/etc that do this?

Thanks!

The easiest (and cheapest!) way is to use your smtp server to send a mobile email.
The host varies by service and can be found on google, but for example, bell mobility would be
tendigitnumber@bellmobility.ca

Most of these should still be good. I know for certain the one for T-Mobile is.

Well that should help! (assuming you've got an American demographic)