Systems, methods, and software for operating communication systems are provided herein. In one example, method of operating a communication system to establish secure communications between a first user device communicating in a first communication network and a second user device communicating in a second communication network is presented. The method includes, responsive to a communication request received from the first user device, establishing a secure communication link between the first user device and a first security node. When a second security node has a security relationship established with the first security node, the method includes establishing the secure communication link for the secure communications between the first user device and the second user device using at least the security relationship between the first security node and the second security node, and exchanging the secure communications over the secure communication link.