Does a GSMV4G work on a with a VISTA-21iP?

If you wanted to add an AlarmNet GSMV4G cellular alarm communicator to a Honeywell VISTA-21iP internet security system it is possible. You would simply connect the GSMV4G to the VISTA-21iP using the same procedure as you would when installing a GSMV4G on a VISTA-20P. However, since the VISTA-21iP has a built-in internet alarm communicator, you will need to deactivate the internal IP communicator so that the security system will use the external GSMV4G as the alarm communication path instead.

This is not a very popular setup and should usually not be considered when designing a new security system. As the VISTA-21iP security system has a specific cellular communicator designed for the 21iP called the VISTA-GSM4G, most people will never install a GSMV4G on a VISTA-21iP. Since you have to turn off the internal IP communicator, most people that want to use a GSMV4G just go with the less expensive VISTA-20P control panel. One reason that this setup may be used is if you can't get an adequate cellular signal strength where an existing VISTA-21iP control panel is located. By turning off the internal IP communicator and connecting a GSMV4G cellular communicator in a remote location away from the VISTA-21iP, you will be able to get a good cellular connection to your panel.