If you hear an airline callsign while monitoring the civilian aero freqs and want to find out which airline it belongs to, check out this page on Wikipedia:-http://en.wikipedia.org:80/wiki/List_of_airline_call_signs
If you need a complete list of aero callsigns, you can find the official FAA contractions list, dated 22 Dec 2005, in PDF format at http://www.faa.gov/regulations_policies/orders_notices/air_traffic_orders/media/7340.1Y.pdf.