well, not directly.
but if your paging rate (from nss counters) is low, it might be due to users not being able to be paged while in PTM.
also, from BSS counters, you can count how many “GPRS suspend” occur. It means that either the MS in PTM has setup a call or received a call (through paging).
I don’t see other ways to count it…
Regards
pix