based on running navizon (gps+wifi+cell data) and playing music over bluetooth, I've never seen more than 850mah being consumed by the phone. although I belive schettj may be right as navizon is only discovering wifi, not actively transmitting data.
I think it's related to heat. ie, the battery will stop charging when too hot, and this may effect the current given to the phone (I need to test this more, but my car charger is only 500mah)
edit; current readings based on
nuePower CPL