Actually, this type of stuff has already been done in the Amateur Radio community. There is even an example of some perl code that uses Win32::SerialPort to communicate with a pager.

Of couse, this is an amateur set up and you will need a license to do this in the amateur bands (as stated on the page). Not sure if you are doing this for fun or as a proof-of-concept for something professional. In the latter case, licensing is going to cost you some $$$. If you want to experiment though, and you don't have a license, locate your local Amateur Radio club (there is always one nearby) and get a licensed operator to work with you. That will make it legal.