For jet operations -
No significant 'event' occurs at V2, and calling V2 would be totally pointless.
V1 and Vr ARE significant 'event' speeds, and should be called.
At V1 the aircraft transitions from the 'NO GO' to the 'GO' state, and the call establishes this altered status in flight crew's awareness. The V1 call is so important that modern aircraft incorporate an automated V1 call from the FMC to cockpit speakers.
Vr is a significant 'event' speed, at Vr the PNF calls "Rotate" (or something similar), and the PF executes the rotation of the aircraft to become airborne.
V2 is a very important speed, but no event takes place. It is the speed which is achieved by 35 feet following engine failure, the minimum speed for initial climb-out etc. A PNF call of "V2" would have no meaning. A PNF call if speed was below V2, or too much above would be appropriate.
In times of old when I flew DC3's, we did call V2, because V1, Vr, and V2 were all incorporated into the one speed. Simpler aeroplanes, simpler times.