we have a MP5000 and 2 FX-II systems set up in 3 different buildings, all connected using gateway blades. I would like to page from one building to the other, or all three at once.
does anyone know (if possible) if the systems can be configured to page the other buildings? I have looked at the paging zones, but they only include the local external port and the local extensions...
Any help here would be greatly appreciated

Check out the ip paging adapters that are available. Never used one but they are out there.

You can feed an IST port into an LST port at each location and modify ARS digits to get what you want. This would allow only one building to the other, not all three at once.

We had the exact same setup and used the Valcom IP adaptors and the worked great

I have it working using nah's method. The customer is happy with it. They are networked with the Hub in Jersey then NODES in Palo Alto Cali, and Pompano Beach Fla.