callevent=yes in the regular chan_sip makes asterisk advertise hold/unhold events for sip channels. It is not a mandatory feature, but nice to have.

I do not know if pjsip advertises the same events without the need to set that or not. You will have to test. If you can start fop2 in debug level 1 you can trace all ami events and see if hold/unhold are reported also:

service fop2 stop
cd /usr/local/fop2
script capture.log
./fop2_server -X 1

log into fop2, dial with your phone over pjsip to someone, put them on hold , then unhold and hangup.

ctrl-C
exit
service fop2 start

at this point you have the capture.log file to check for events on your call.

Best regards,