Bear with me here - very new when it comes to Lync :)
We have a very simple installation up and running right now, with only Lync software clients installed. I've now been requested to install two Polycom CX3000 conference phones.
It looks like these requires a phone number to work correctly, so we're going to order a small SIP trunk for Lync plus two voice CAL's so that these two devices can make outbound/inbound calls outside the Lync organization. That should be nice and simple to set up.
The question however is how intra-traffic is going to be handled between regular Lync users with the Lync client and the conference phones. Will they accept "Lync calls" as Microsoft calls them - as in calls without any telephone numbers? Can you mix attendants in a call where some are via enterprise voice, and others are via regular lync calls?
When you creat a conference phone it will appear as a contact which LYNC users can make calls to just like any other contact. The conference phones will be able to call any LYNC enabled users and if you configure it, make calls to the regular PSTN.
You can also invite the conference phones to meetings which simply makes the phone join the meeting at the set time.
If you want to have users from the PSTN participate in your conferences you will need to configure dial-in conferencing on your Lync front end.