We have two MultiVOIPs with one MVP110 configured as a client and the other an MVP120 configured as a host. So, my question is, are they compatible, (i.e can they communicate)?
As long as the MVP110 and MVP120 have the same firmware they are compatible. They both require h.323 or they both require proprietary firmware to be compatible. They will be able to communicate, providing the host has 2 entries in the phone book. One for itself and one for the client. The client should also have the phone book download to itself before it will be able to call the host. Check the client to assure it received the phone book entries from the host.