Add-on GSM dialler/texter options.

My mother has an old Airtech CS350 alarm system its simple and still serviceable, more importantly my mother who is elderly can set and unset it ok. I would rather upgrade it than replace because my mother will struggle with the change. At present I'm working away from Dublin a lot and want simple remote monitoring of her alarm, just a GSM unit with a payg sim to send a text if the alarm is going off. The house has no internet and the box is miles away from a phone point. In my day job I work with industrial automation so 12v relays & switches shouldn't be too big an issue for me. I've seen GSM modules on the internet for less than €100, but they were UK network only, can someone recommend me a simple low cost GSM board that will take a sim or alternatively a wired dial-up unit that can be triggered via a wireless switch in the panel.

Cheers.