Require agencies that have access to interoperable radio systems to include their use in their written policies.
I work as a police/fire dispatcher for a local agency in Colorado. I'm a big fan of our radio system. The mutual aid channels are set up well and easy to understand. Working in the Denver metro area, I have the ability to communicate with any agency in the state.
The big problem is that we have the technology, but we don't use it. While the fire department makes use of mutual aid and other agencies channels when participating in a mutual aid event, our police department doesn't. I don't think my agency is alone in this.
Law enforcement officials need to train with their radios AT LEAST as much as they train with their firearms.