This was opened by Darren Taylor on the Microsoft Graph UserVoice site and it did gather 19 votes there as can be seen here.
This is the original text:
We wish to automate linking call/meetings held on teams to a CRM, we can get a call data via:
But if a participant is an external user, or guest a tenant/or random ID is shown - but I cannot see any way to lookup who this was.. as their data is on an external tenant or they were a guest.
Adding an email property here would allow us to link to participants to customer records by email giving us invaluable interaction data that we used to have when using a standard phone system to hold conferences/meetings.
Basically, if we can see the external user's name/sip while in the Teams meeting, this should also be available through the Graph API. "External User" and the Guid are of no use.