Hi Bill, - I've found a resource that might help. It is a sequence of modem AT commands that let you send SMS message. However, the challange will be to find a modem that supports this AT commands extension. I have tried a few internal modems with no luck. I recommned getting in touch with some major modem vendors (search the web) to find one.
Here is the link:
http://www.option.com/2/support/SMS.htm