I am curious to know if it is possible to have two startalk flashes or CP's or a combination of a STLK and CP on the same MICS. I have a client that is looking to separate a regional office from a local office and I would like to offer them this solution.

No - you cannot.
Yes you can have two Call Pilots. Or at least I think I have heard this can be. But one is for Voice Mail and the Other would be for Call Center.

But not two VM for two companies

NTlayoff is correct about the two Callpilot 150's (one for vmail and one for call center). The only thing you cannot do if you have two call pilot 150's, is transfer voicemail messages between the two.

I havnt done it but I heard you could run two VM Fashes on one KSU

Flash - No
Call Pilot 100 - No
Call Pilot 150 - Yes, as pts technician stated

Why not use 1 CP150 with different Tables?

If that's not what you want to do, only other option is a N.A.M.

They have a flash now and was curious if I could add a CP 100 for the other department. I am recommending a CP 150. Just curious really. I thought with the ability to select F-codes that you could possibly setup 2 and just program the call forward and login etc.. for a specific vm.

As MT mentioned you can have 1 Flash with two different Tables and two separate Tree with appropriate Greetings for each one and not to force client to buy another VM