1. A method of determining a position estimate for a wireless terminal, comprising: obtaining an initial position estimate for the terminal using a first position determination scheme based at least in part on one or more signals from a first wireless communication system; obtaining a set of one or more measurements using at least one additional position determination scheme based on at least one signal from at least one additional wireless communication system that is distinct from the first wireless communication system; and updating the initial position estimate based on the set of one or more measurements, wherein the set of one or more measurements is a partial set of one or more measurements that is insufficient to independently derive the position estimate for the terminal with a threshold level of accuracy using the at least one additional determination scheme, or wherein the set of one or more measurements is a complete set of one or more measurements that is sufficient to independently derive the position estimate for the terminal with the threshold level of accuracy using the at least one additional determination scheme.