From time to time the instruction would be something like "Contact Hong Kong Center" or "Contact Taipei Center" followed by a series of digits, which she assumed must be a radio frequency. Whereupon the pilot would identify himself and repeat the instructions as usual, and then sign off with a "Thank you" or "See ya" or "Out," never to be heard from again. At least on this channel. So she figured that these were outbound aircraft being handed off from one air traffic control center to another.