I came across this when connecting to the Lync client dial-in Conferencing Settings.
As it reads the information from Active Directory I assumed there was a field somewhere I needed to complete that I had missed – not the case. I then wondered if it required a custom AD object creating – also not the case.
Turns out that you need to add the extension details to your Tel URI number in OCS/ Lync. This is done by adding “;ext=xxxx” after your Tel URI. i.e: tel:+441785111111;ext=1111 (we are obviously using a 4-digit extension internally).
Once completed i know get my extension listed after reconnecting to the dial-in conferencing settings.
What does this mean. Well, it means that if you are connecting to a conference call over your landline/mobile etc. that instead of having to enter your entire phone number as an identifier, you can simply use your extension number.