Being able to talk to each other != effective communications
Most of these interoperability schemes try to push the level of communication down far too low.
As a rule, a police officer does not need to talk directly, by radio, to a firefighter. They can follow their normal chain of communications and have the dispatchers organize and deliver the messages in a manner everyone understands. There may need to be improvements in how that dispatch-to-dispatch communication process works, but that's where the improvements can be focused.
On certain tactical assignments you can coordinate in person whose going to do what, and hand out compatible radios to all involved.
There is, no doubt, the need for compatible communication equipment between senior managers. While this often can be accomplished by this wonderful interoperability device called a telephone, there is a need for radio systems as well. In my state that is the I-TAC system that allows local police & fire chiefs, state agencies like State Police, Environmental Protection, and Transportation to all have a common radio channel assigned to coordinate their activities. I-TAC is 800mhz; there are also V-TAC (VHF 140-ish mhz) and U-TAC (UHF 400-ish mhz) standards out there to allow national capabilities.
Most of this radio stuff is far to complicated and does not meet the real needs. We need systems like I-TAC to coordinate between managers at multi-agency incidents. We need a Resource Management System to coordinate responses to disasters -- no radio system, no matter how fancy is going to overcome the problem that disasters overwhelm human's abilities to collect and sort through the volume of information generated. That's a computer problem, to allow local agencies to punch into the computer their needs, have the computer match the requests with available resources, and simply give a human the final approval to make sure the computer program didn't spit out something wildly unrealistic.
Part of the shame of Katrina was you had requests going unmatched becasue agencies were relying on inter-personal phone calls from one contact to another, and on faxing lists to one another. State Emergency Management Agencies which are responsible for coordinating large resource requests in such situations failed not due to communication technologies but because people were at their human limits. They need much better computer systems, not radios.