Micheal VK3ZEA shows some interoperability.
Asterisk is a powerful open source VOIP telephony platform. There happen to be a few hams heavily rooted in the project. So naturally there is a module called app_rpt for integration of 2-way radio systems.
For more info see:
What Micheal is showing, involves some rather complex configuration. But much of the open source software that powers what he is showing has come along way. So I expect even further down the road, this will be child's play.