That's a big question.
Last question first: You might be able to use them via AudioCodes' Sip Phone Services. This is an application that runs on a server and basically converts between SIP dialects, in this case between Alcatel and Lync. You probably won't get 100% feature parity
between the buttons on the phone and Lync, but the main features should work (dialing numbers, hanging up, talking.)
As for the main question. SInce you are putting the AudioCodes upstream from your Alcatel then yes, you should be able to fork calls between Lync and the Alcatel. Let's assume you have your only PRI connected to the AudioCodes, the Alcatel connected via a
SIP trunk, and then Lync connected to the AudioCodes via SIP.
As a call comes in to the AudioCodes, you can fork the call and have it ring both Lync and the Alcatel handset. When the user answers the call, the AudioCodes will drop the call to the path not used to answer and keep the call up to wherever the call was
actually answered.
What starts getting dodgy is as you migrate users between Alcatel and Lync and wanting to keep the same extensions between systems. It's easiest to just move the user to Lync and either give them a new extension, or move the extension to Lync and remove
it from the Alcatel altogether.
Talk with your AudioCodes reseller about these options. There is cool stuff out there too, such as the AudioCodes knowing (via AD integration) if a user is enabled for Lync to route the call to Lync without having to do any manual routing on the AudioCodes.
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