I presume that by:
"One of them is in Intercom Group 1 and the other is in Intercom Group 2 because of space limitations."
You mean that you wanted an intercom group that is greater than 32 members.
That sadly, is the limitation. No more than 32 people be members of a specific intercom group.
And, no. If you are not a member of the intercom group, you can't call someone in it. So a person in intercom group 1 can't call a member of intercom group 2.
If your goal is to provide a speedier way for a group of people to dial each other, perhaps a group dial list would be a good choice. It can have many more members, would dial pretty much the same way a dial-intercom would, and could simulate auto-intercom if you put a list and member on an abbreviated dial button.
The only downside is that you won't receive the special intercom notifications. (Flashing auto intercom buttons and special beep-ring.) The upside is, if the intercom-called party isn't available, the calls can go to coverage. (Which intercom calls will not.)
Carpe dialem! (Seize the line!)
