I want to set up my security system to call out wireless to the monitoring center, at the moment it is calling out on a landline which I want to disconnect, I know I need a voip router connected to my security system but how does the computor or modem receive the signal and how does it dial out?





You should talk to your security system provider. They may offer alternate ways for the system to connect, but I don’t know of any way other than a landline for that to work.
If you were to use VOIP, I think it will work as long as the phone cord that once connected to your landline gets connected to your VOIP router.
The best solution probably is to call your security system provider. They will have ideas for you.
Perhaps the easiest way to do this is to purchase and install a GSM communicator. You’ll want to check first to be sure your system is equipped to handle it, but if it is, this would solve your problem. A GSM module is used to communicate between your system and your central monitoring station, or a cell phone or private number (if you don’t have monitoring). Many people buy them, even if they do have landlines. That way, if the landline were cut, the system could still communicate with the monitoring station. Good luck. The link below is to one particular GSM module that will work with any system (assuming the system is able to be GSM equipped). The link below that is to an article explaining what GSM actually is.