<rant>
One of the biggest problems facing public safety communications in the U.S. is the fact that it is now being driven by cost and politics, rather than a properly done needs assessment and engineering considerations. I've been in this business long enough to see consolidation of dispatch centers, centralization of systems to reduce redundancies, and then see the pendulum swing the other way. Agencies that consolidated are splitting off to do their own thing. 20 year old agreements to share systems are falling apart.
What concerns me about centralized systems is loss of local control and autonomy and, because money becomes the driving force, a system architecture that presents too many single points of failure is created. Lose a critical switch, or a critical link someplace, and you don't lose communications in just one jurisdiction, you lose it in 50. Proper system design can mitigate a lot of this, but quite frankly, I have yet to see any agency be free flowing with enough cash to design and built a system that's robust enough to take whatever can be thrown at it. The survivability and redundancy is lost, replaced by features that aren't really NEEDED. And building a non-redundant, non-survivable common system for many user agencies is simply not acceptable, in my book.
While having a centralized 911 PSAP and dispatch center could be an over all cost savings, it comes at a very high price. Local dispatch centers are staffed with local residents, who know the streets and neighborhoods. The cops on the beat are well familiar with their areas, their dispatchers need to be, also. Public safety is not a service that can, or should, be farmed out to a centralized facility like a help line call center.
Addressing interoperability, what's missing is the discussions of who NEEDS to talk to who, and what do they need to talk about. A great deal of the interoperability that takes place isn't done on the radio. The cops don't need to talk to the trash truck drivers, who don't need to talk to the dog catcher... and so on. Police and fire speak different languages, almost. They have different needs, a different command structure. In a major incident, it's their command staff that need to be talking.
Having a conventional common air interface would suffice for most interoperability situations. It can cross manufacturer platforms, and if plain language is used, can cross political boundaries as well. But political agreements and operating procedures need to be in place before systems are built.
The bottom line is, while the financial part of the equation is essential, it should not be the main driving force behind a particular systems architecture. If the needs assessment determines that a central consolidated dispatch center is the way to go, then so be it. But it shouldn't be done just to save money.
</rant>