I was working for one of the "big" 3 planning the rollout of IPv6 in their cellphone network. They stopped the project due to budget concerns. Doesn't seem to be too high of a priority for them.

Only the police is driving ipv6 hard in the carrier market (since tracing back connections via CGN is hard if not impossible).

There is little to no incentive to change a well working network, it makes (business) sense to introduce v6 in the upcoming G5 but not in the running setups.