1. A method for use in completing calls from first and second wireless telephones each having a MIN, said wireless telephones being served by respective first and second wireless carriers, the method comprising the steps of: receiving at first and second mobile switching centers belonging, respectively, to said first and second wireless carriers, requests for completion of a wireless call from each of said wireless telephones; establishing with an authentication platform, from each of said first and second mobile switching centers, respective first and second voice channel telephone connections, said authentication platform serving said first and second wireless carriers, if said first and second requests originated from wireless telephones belonging to a group of predetermined MINs; supplying to said authentication platform said MINs of said first and second wireless telephones, said MIN of said first wireless telephone being supplied over said first telephone connection and said MIN of said second wireless telephone being supplied over said second telephone connection; transmitting respective challenges from said authentication platform to each of said first and second wireless telephones, via said first and second telephone connections and said first and second mobile switching centers of said first and second wireless carriers, each of said challenges being developed by said authentication platform from respective secret keys stored therein in association with said respective MINs of said first and second wireless telephones; and denying, by said authentication platform, said first or said second call requests for which a proper response to its respective challenge is not received.