This document describes the accepted and recommended formats that can be used for FindMe IDs.
FindMe ID Formats
A FindMe ID can be formatted in any manner desired. For example, you can use an IP address, or a string of characters or numbers. If a user can dial it from an endpoint, it can be used as a FindMe ID.
However, Cisco recommends that FindMe IDs take the form of Uniform Resource Identifiers (URIs) for networks that currently include Session Initiation Protocol (SIP) or might include SIP in the future.
While the use of non-URI formatted FindMe IDs can work in an H.323-only deployment, it can get complicated in a mixed or SIP-only deployment. This is because SIP endpoints can only register with an Address-of-Record (AOR) in the form of alias@domain, and SIP dialing can only be completed with the use of URIs. If you dial an alias without a domain from an SIP-only endpoint, the endpoint appends its own domain to the alias before the request is sent to the Cisco TelePresence Video Communication Server (VCS).
For example, if your FindMe ID is 123, and a user dials 123 from an H.323 endpoint, the call is sent to the VCS as 123. This is recognized as a FindMe ID and resolves to the aliases that you have configured for it. This is as expected. However, if 123 is dialed from an SIP-only endpoint (which is registered as firstname.lastname@example.org), the call is sent to the VCS as email@example.com. In this case, the VCS does not recognize the FindMe ID, so the call is not placed.
You can set up a Call Policy on the VCS in order to strip the @example.com from all inbound calls, but then you are not able to call an SIP endpoint with its AOR, only via a FindMe ID that resolves to the SIP AOR.