I was just wondering if I can use IP telephony to connect to the alarm system. I know that it works with PSTN but I have my telephone via broadband modem(however I use a traditional telephone set connected to the modem

Visonic panels are not compatible with I.P lines (digital lines)

It can work, but cannot guarantee reliability.

The analogue to digital conversion is not always successful, therefore cannot guarantee any success when using digital lines.

 

Its unlikely to work as sip etc is designed for voice not data. If you wish to use ip signalling then id advise a panel that supports it natively