1. A method for interfacing between requesters of availability information and sources of availability information, comprising: (a) receiving availability requests from the requesters; (b) prioritizing the availability requests; (c) processing the availability requests according to the associated priorities; (d) selecting one or more of the availability information sources to be queried for each of the selected availability requests based at least in part on one or more factors associated with the requesters, the requests, the requested availability information, and/or the availability information sources; (e) querying the selected availability information sources; and (f) providing results from the querying to the requesters.