This article relates to Cisco TelePresence Video Communication Server Expressway.
Q. What format can or should a FindMe ID take?
A. A FindMe ID can actually be anything you like - an IP address, a string of characters or numbers - anything a user can dial from an endpoint can be used as a FindMe ID.
However, we recommend that FindMe IDs are in the form of a URI for networks that currently include SIP or may include SIP in the future.
While the use of non-URI FindMe IDs would work in an H.323-only deployment, it would get complicated in a mixed or SIP-only deployment. This is because SIP endpoints can only register with an AOR in the form of alias@domain, and SIP dialing can only be done using URIs. If you dial an alias without a domain from a SIP-only endpoint, the endpoint will append its own domain to the alias before the request is sent to the VCS.
So for example, if your FindMe ID is 123 and somebody dials 123 from an H.323 endpoint, the call will be sent to the VCS as 123, which will be recognized as a FindMe ID, and will resolve to whatever aliases you have configured for it. This is as expected. But if 123 is dialed from a SIP-only endpoint (which is registered as firstname.lastname@example.org), the call will be sent to the VCS as email@example.com, which the VCS won't be able to find, so the call will not be placed.
You could set up Call Policy on the VCS to strip the @example.com from all incoming calls, but then you wouldn't be able to call a SIP endpoint using its AOR, only via a FindMe ID that resolves to the SIP AOR.
Using FindMe IDs in the form of a URI prevents these issues.