Normally, the trouble is that VOIPis a good medium for voice, not for data.
I am not sure, but I do not know of any comercially available service that provides modem capabilities .
I have seen the option on some high end gateways, with many lines atached, but I do not recall any on or two ports terminal that could do it.
Some burglar alarmrs are nothing else that a device that sends some very basic audio tones over the phone line. Completely non-standar.
Thos hava better change to work that the newer, better type.
Maybe some alarm guy reading this posting could clarify the point. I will not bet any money yet.