While this apparently* works, if you want a solution that is reliable and widely compatible I recommend use of a serial port SMS modem. * I haven't tried it.
There is of course always the option of just tethering an old phone to a Linux or Windows machine.
I've played around in the past with an old Nokia, using a Linux-compatible knockoff DKU-5 cable (I bought mine from http://www.affordablecomputers.co.nz/ but I assume other retailers will have them).
There's a whole suite of tools available for Linux to interface with a phone in this configuration and send SMSes. Throw an MTA and something like monit in to the mix, and you have a very cheap SMS monitoring solution that doesn't depend on any external ( besides the cell network of course ;) ).