I want a device that acts as an SMS/GSM node, sending messages directly to my users' cell-phones. It should either be something that I can talk to via ethernet and TCP/IP (using something like SNPP preferably, but any protocol I can decipher will do), or alternatively be something I connect to my Linux box with some software and it transmits whatever the USB/Serial/Parallel/whatever connection tells it to.
Solutions which include the phrase "... and it connects to our web server ...", "... and it will e-mail through your GSM provider's mail server..." or "... it connects to the provider via the Internet and delivers..." are not acceptable. *grin* The whole point of the exercise is "how do I alert the staff that the mail server, internet router, etc., etc., are down?"
Nokia has these Mobile Phone Cards (PCMCIA), which obviously can speak SMS/GSM etc. etc. -- problem: I don't know if they can be accessed from *nix
For relatively low volume needs, just use a regular cell phone. Most of them can be connected with a serial/usb cable, and you can send SMS messages using AT commands.
My Sony Ericsson T610 does this (albeit via Bluetooth, I haven't tried serial).
http://smstools.meinemullemaus.de/