We used the linux software sms_client - I believe it's packaged with many distributions, but can also be downloaded from here. It uses a modem to contact a message centre directly - a list of UK message centres can be found here.

A couple of caveats:

1) The message centre allowed you to send the message to up to 3 mobiles in a single call - so for a long list of notifications, you will have to make multiple calls.

2) In the UK, calls to these centres are rated on your phone bill as mobile calls - this was cheaper for us than signing up with one of the TCP/IP based services because we are a telco.

Depending on the number of messages you need to be able to send, you might find this solution we used is adequate.