If you need to have a phone in your office that only calls a specific number when picked up, the the Yealink's Hot Line feature is for you. Most people do this in lobbies or shop floors and point them to auto-attendants that give the caller instructions. Here are the steps to setup the Yealink phone for Hotdialing:
1. Go to the Menu (Each model may be different see the guide for your model)
2. Choose Option 2 Features
3. Select Option 5 Hot Line
4. Enter the number or extension to Hot Dial
Now when someone picks up the phone or speaker phone the phone will automatically call that extension.