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It's more effective to spend the money on SMS messages. Mobile providers are forced to use very aggressive anti spam measures, which can add significant delays in message delivery.

Recommendations on software and modems?

Easy enough to build, here's one I made earlier http://www.bogons.net/pics/x1gsm.jpg ebay/old Sun X1, serial gsm modem, qpage = OOB alarms Sun X1s are cheap, low power and have good management already so you can throw them in remote places brandon