It's interesting, Roseville is sorta between a rock and a hard place. Their own county is VHF, and going to a P25 Trunked system... their big neighbor (Sacramento) is 800 trunked, and going to a 800 P25 system. It leaves them with 3 options:
1a- Stay with 800 and go P25 Trunked. The issue with that is that once you get outside of Roseville (in Placer County) you're going to lose coverage. Therefore you cannot easily assist with a Mutual Aid situation in Placer County, however you can help in Sacramento, as your radio will be compatible with their system. Pros: You don't have to replace your antennas in your cars since they're already 800 mhz, so you save some money there. Cons: you're building your own p25 trunked system... that's expensive.
1b- Stay with 800 and go P25 Trunked, basically same as above but get APX7000 multiband radios... Which are MASSIVELY EXPENSIVE. We're talking $7,000 per Public Safety user. Plus the cost of upgrading your infrastructure to P25 Trunked. Personally, I'm not sure that the usually conservative Placer County taxpayers are willing to pay that much.
2-Join Placer County's VHF P25 Trunked System. I think this is the best solution personally. I don't know how often Roseville assists with Sacramento compared to Placer County, but I'd venture a guess that they assist Rocklin (who is VHF and will be on the P25 system, at least patched/simulcast) and Placer County more often. You'll have to pay per subscriber (usually how it goes when you join someone else's system) and you have to pay for new radios AND new antennas, however it's easier to contact CHP, surrounding county agencies and you're not paying for as much of the infrastructure... the county is.
I just hope that Roseville doesn't fall into the trap that Oakland did and go with a low ball offer from Harris, regret it and end up with a useless system and (eventually) joining a regional system after wasting all that money.
the preceeding post in no way reflects the views of anyone except myself.