Speaking of alarm systems over VoIP, here's a story of an alarm company that was sued by the estate of a murdered woman because her alarm system failed to notify the central station when the attacker broke in. It turns out she had switched to VoIP a few weeks earlier, which caused problems: http://www.security.honeywell.com/hsc/documents/alarmorg_VoIP.pdf
Bottom line: I'd think really hard before switching an alarm system to VoIP. When we switched the company to VoIP, I was able to get a very inexpensive measured line for our alarm system. (We also use it for incoming FAX, because it works.)
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