FlightInfoEx will return details about all recent instances of flight number, including its origin, destination, and route.
However, we always canonicalize idents to ICAO when possible, and do not provide mechanisms for outputting in IATA format. We encourage transitioning to the use of ICAO instead of IATA, since there is less ambiguity, fewer conflicting codes, and it is the system actually used for flight operations. Be aware that in some cases, we cannot automatically convert IATA requests and you may receive confusing or unexpected results. (For example, JetBlue’s IATA code is B6 which overlaps with a segment of Chinese aircraft registration numbers–using their ICAO code of JBU eliminates the ambiguity.)
Sure I understand the ambiguity that is introduced with IATA identifiers - however it remains that the Airport community (including airport FIDS) still display the IATA information. For lots of airlines, the flight number is consistent across the ICAO/IATA mapping and so the IATA flight ID is easily deduced (i.e BAW123/BA123).
However, in many instances, this assumption is incorrect. The IATA and ICAO flight numbers are different - which is what I hope FlightAware could solve (along with route).
So you have nothing that will return a route and an IATA id for a given ICAO Callsign?