You can create up to 256 intercom groups per standard and up to 1024 intercom groups with SA9035 - Increased Intercom Groups on one server that runs Communication Manager.

Each group can contain up to 32 extensions in it.

You can assign the same extension to different groups.

Intercom calls are possible only between extensions in the same group.

Any group member with a feature button for Dial Intercom can make an intercom call to any other member in the group.