As of Feb. 11, 2005, mobile satellite providers were required by the FCC to provide 911 service within the U.S. See following link for a write-up of what 911 services Iridium provides to it's subscribers: http://support.ocens.com/downloads/d...%20service.pdf
Bottom line for Iridium is you theoretically need an active sim card to place a call whether it's for 911 or a regular call(at least in theory, I wouldn't want to depend on an uninitialized handset without a sim card to place any call). To be fair Iridium and other providers are complying with FCC regulations which are written differently for satellite than for cellular providers and the 911 call will not be charged to the subscriber. Plus Iridium does have some regional discount programs (e.g. Alaska, Canada or Africa) and prepaid services. Anyway, it would be desirable to have a return phone number in an emergency situation for rescue services to contact the party in distress while they are en route or if they need additional information.
Another satellite emergency solution would be a SPOT satellite telemetry handset(no connection to Iridium; it uses different satellites that are part of the GlobalStar network). Very basic but it provides location tracking and an emergency transponder for $100/year. http://www.findmespot.com/en/index.php?cid=1300