This isnt that, for 6b dollars, you're unlikely to cover more than a handful of major metros, figure its 250k for a greenfield site, 100k for a co-located one, plus associated core network costs, for a national network you'd be looking at more like 100b+.

Beyond that, most communications between the field and dispatch is narrowband, not wideband, and this is unlikely to change in the near future - if you think the police agencies are relying on public internet access now to do mission critical dispatch, you'd be wrong.