I did this. Bought a Motorola RAZR on eBay, plugged into a FreeBSD box and called it a GSM modem. Since we were monitoring if the network was down among other things, the pages would go out through the "GSM modem" since the fiber connection couldn't be relied on to be up. Paid like $10/month for a text-only phone plan. Worked great. The USB connection to the FreeBSD server keep the "GSM modem" continuously charged as well.