So as a First Officer you could, for example, fly a codeshare route operated by Alaska Airlines from KSEA-KSFO in one of their 737-400's or from KPDX to KGEG in a Dash 8-Q400, but you cannot fly a Mexicana codeshare from KDFW to MMMX in one of their MD80's because the flight doesn't end in the US.1. - Pilots ranked as Captain and below may fly any code share flight which uses equipment for which they are qualified and which departs and lands within the United States. For example, Trainees may fly code share flights which use any commuter turboprop aircraft. Second Officers may fly scheduled trips which use any of the regional jets (such as the ERJ & CRJ series) and First Officers may fly code share flights which use MD 80, 737 and A320 aircraft.
A codeshare flight will have an AA flight number and a different flight number assigned by the operating carrier. You can use either one, but you have to let your Hub Manager know where you found your flights so he can verify that they are valid. It also makes it easier if you stick to one source, although that is not required. i.e. if you use flights from the real aa.com time tables then stick to those for your entire FREQ.
I hope that answered your question.
On a side note, if you are flying online it doesn't matter what callsign you use on vatsim. You can use the AA codeshare flight number, or you can use the actual carrier's flight number. Say your bid lists AA7517 KSFO-KPDX. That is actually Horizon Airlines flight #2520 (QXE2520) and it is a CRJ-700 route. You can fly that on VATSIM as QXE2520, submit your FREP as AA7517 and list in the comments "Flown online as QXE2520". As a Hub Manager, it is a lot easier for me to verify a flight that someone completed on VATSIM under whatever callsign than it is to hunt down all the real flight numbers for codeshare routes. That generally means quicker approval times for you as a pilot.
