Yealink T48, Mutiple lines - Deny incomming calls.

[jolouis]

Why do you have two extensions setup if this is what you are after?

Typically in this kind of scenario you setup a single account/extension, and then assign a few line keys to it. You then disable call waiting on the phone. This allows you to only get one incoming call at a time, but if you need to put the caller on hold and dial out to somebody else for something you can still do that.