When you manage the profile properties...

And you edit a profile property,...

In a sction called "Active Directory Import Mapping" you can map it
to an active directory property using a pick list that includes
about a thousand AD attributes from which to choose.

However,...

When you install Live COmmunication Server on your domain
controller,...

and you extend AD to include the LCS attributes, there's a tab for
Live Communications that includes a field for SIP URI:

That's where you enter the URI Session Initiation Protocol.

We've got a Windows Admin that's hot to use this but we can't find
the SIP URI in among the thousand or so options in the pull down
list.

So the question is, where does the that pull down list come from and
how do we get new values in it?