3 servers call routing... How do I get between switches

So I have 3 servers all runnin the same version of asterisknow. I have a main server in our corporate location with several extensions and two servers connected via vpn in two separate locations. Both of the sattelite servers are connected to the main switch via IAX2 trunks. The main location is extenstion 2xxx, the other two locations are 3xxx for one and 4xxx for another. I can call 2xxx from either of the external locations, I can call 3xxx or 4xxx from the corporate location to get to either of the sattalite locations… but I can not figure out how to get the sattelite locations to call each other through the corporate location. So I want the corporate location to be the go between.

Opening the VPN to add an IAX2 trunk between the sattelite locations is not an option, the translation has to happen in the corporate offices. I know I can transfer calls between them from coporate so there has to be a way to dial 3xxx from 4xxx and be able to connect the two.

Thanks for any help anyone can provide.

If the trunks are all in the from-interal context this will happen automatically

Worked perfectly, thank you!!