If I call Bob on my GXP2000 or if Rita calls on her GXP2120, call goes through fine.
If we call and turn on speaker phone, Bob cannot hear us talking. We still hear him fine.
When Bob calls us, he can talk fine. When he turns on speaker phone, we cannot hear him talking any more and he can hear us fine. (so the same thing as us calling him basically)
We're using the Freepbx distro, nothing fancy set up on that or the phones at all.