I would suggest that since our individual and anecdotal experience with call control and related state machines will result in various descriptions that could take some time to bring to consensus, that to shortcut the process:
1) For each type of call, we reference and leverage the applicable standards, e.g. for GSM the 3GPP Stage 2 spec family for "TS 23.018 Basic call handling; Technical realization" [1] and for IMS "TS 23.228 IP Multimedia Subsystem (IMS); Stage 2" [2]
2) While recognizing that what is possible in terms of PLMN call state knowledge by clients is bounded by standards, seek also practical advice from experts on call control who are familiar with the APIs that chipset manufacturers expose to OS platforms: these are the same APIs that Web-based device vendors will need to use, and will further limit what is exposable through the API
3) For Sysapps, seek explicit state machine proposals in SDL or state diagram form, which can abstract the above in a form suitable for modeling in Web IDL
Otherwise this is likely to be a long and complicated process of education and re-education, as people try to reverse-engineer how telephony works today.
[1] http://www.3gpp.org/ftp/Specs/html-info/23018.htm
[2] http://www.3gpp.org/ftp/Specs/html-info/23228.htm
Thanks,
Bryan Sullivan