Great, thanks for that information! I appreciate your help. It makes sense that you can omit your position and altitude in the initial call up since they have you on ADS, but I wasn't sure. In my use of it so far, it has been a big help, particularly in the singapore FIR whre there's a compulsory reporting point every 100NM and you're on the same HF frequency as 2 or 3 ATC agencies and a few dozen a/c! whew!
-RP8