At Ray's Pager Sales, you can pre-order the G4 with the P2 update for the same price as you can buy the G4 today. That offer ends March 31, and units will ship around March 31.
Unication G1 G4 & G5 Pagers - Fire & EMS Services - Ray's Pager Sales
If you can't wait, or already have a G4-5, it is rumored that the P2 update will cost around $100-130.
TRWC control channels are still advertising as only P1 capable, so they still have some Infrastructure work to do. The RWC control channels just started advertising as P2 capable this weekend. You will start seeing some P2 test talkgroups. All radios that use a talkgroup must be P2 capable, or it will revert to P1. I'm guessing there are still a lot of XTS 5000's out there that need to be replaced as I still see Phoenix officers carrying these. Since the FCC pushed back the deadline to move 700mhz to P2, there is no hurry to upgrade. If I were to guess, it will be at least 1 year before Phoenix PD, Mesa PD, Phoenix Fire, or Mesa Fire move to P2. It will probably be closer to 2 years.