The US Army is rolling them out, according to the defense blogs. These 30mm Strykers are really in service so they are fresh off the boats.
It's not a simple conversion from what I read. The hull's roof had to be reinforced although these Strykers don't all have the double-V hull modification.
The other non-30mm Strykers will receive the upgraded CROWS II with a Javelin ATGM launcher mounted on the side of the CROWS, giving them some form of anti-tank/anti-bunker firepower. It's a modification that NATO used for their CROWS II RWS that the US Army is copying in an attempt to increase the firepower and range of CROWS II beyond 7.62mm, 12.7mm, and 40mm grenades.