Electronic Alarms and Home Security Devices - Making a phone call with no phone line

I have a DSC PC1555 home security system. It's not monitored and I don't have a phone line; I do have a cable internet connection. When a problem occurs I would like the system to call my cell phone. Since I don't have a phone line it's a problem. I was wondering if there are any devices that would allow DSC to call my cell phone or send me an SMS over Ethernet (I don't want to sign up for a VoIP plan though). Alternatively, is there a way to have DSC make a phone call over an old cell phone with a pay-as-you-go SIM? (I've seen proprietary DSC GSM modules, but they all require monitoring subscriptions)

The alarm industry is well lagged behind cell phone development. The best fit for your specs is made by a company call ed United Security Products:

http://www.unitedsecurity.com/pages/cellular.html

MrRonFL - Thanks for your help!