Morris 542
being the anorak I am I like to keep a list of these alpha-numeric flights. I currently have a list 2200 flights long. The EZY flights are relatively easy because, as you mention, they ofetn have part of the flight number in them. RYR, TCX and TOM are a little more complicated and bare little relation to the flight number. WZZ however often really confuse me. They used to be relatively simple but have recently become more complicated. I think a flight has a callsign assigned according to the base of the aircraft used and the day of the week.
If anyone else knows how they work them out please let me know.
Andy S