Methods and apparatus to measure market share for VoIP carriers is disclosed. An example method includes querying a plurality of VoIP carrier servers to determine the VoIP carrier server that owns the telephone subscriber number (SN), in response to the querying, receiving a plurality of messages operable to determine whether the telephone SN is found within any one of the plurality of VoIP carrier servers, when the received plurality of messages is at least one of inconclusive or when the telephone SN is not found within any one of the plurality of VoIP carrier servers, placing a first partial call to the telephone SN from a first VoIP number within a first VoIP carrier network, receiving a first signal from the first VoIP carrier network, and based on the first received signal, determining whether the telephone SN belongs to the first VoIP carrier network.