I remember playing Kesmai's Air Warrior on my A500, as well as a CGA PC (May have been EGA or Tandy Graphics...).
Didn't it have an option to dial another user directly for a two-player game as well? I seem to recall comparing it to "Air Duel: 80 years of dogfighting" which had this feature, but memory is a bit hazy...
Have you had any luck finding info?