If we're looking for belt and suspenders solutions (when you lose your primary WAN connection and the cell modems are jammed up...)
You could also hitch up an analog modem to a POTS line, and then let your paging software dial your cell/home number. You won't hear anything, but the CallerID will let you know that your monitoring system is *desperately* trying to get in touch 
Rich Brown richard.e.brown@dartware.com
Dartware, LLC http://www.intermapper.com
66-7 Benning Street Telephone: 603-643-9600
West Lebanon, NH 03784-3407 Fax: 603-643-2289
You could also hitch up an analog modem to a POTS line, and then let your paging software dial your cell/home number.
You won't hear anything, but the CallerID will let you know that your monitoring system is *desperately* trying to get in touch 
You could take it one step further and get an FXO card and put it in a very basic asterisk server. Write a simple program which call be pinged with issue reports as an argument, then pass those arguments to festvox or other TTS application. Output to WAV, convert to GSM, generate an asterisk call file (or write an extension) that calls you on the analog line, and plays you the sound file.
I've done this at several employers. It works fairly well - perhaps better than it sounds. If you can get a SIP upstream that will let you set your CID, then send the calls out that route first, and the POTS line becomes a backup - then if you ever get calls from the POTS DID, you know that you have the original problem, plus you know that the connection to the SIP gateway is down.
Nathan Eisenberg
Correct me if I'm wrong, but shouldn't it be possible to grab SMS via SS7 and feed it into a softswitch or similar like an Asterisk box? All that would be required would be a friendly SMS provider with an "SMS peering" or gateway with the network(s) you care about.
I know Verizon was offering a landline VoIP phone that offered SMS long code support a while ago, but I was never sufficiently interested to examine it further.
DJ