PG Wiki

The Grandstream entryphone can be used for all the following:

• allow access to callers via the front door
• call Sue in the office
• call other apartments

You should have been supplied with a small manual for this, but it doesn't tell you how to use the phone.

Quick User Guide but much of this is probably irrelevant.
Tunstall user guide
Brochure
Datasheet
User Guide
Resident User Guide

Here are some notes on its use:

Tell your visitor to enter the apartment number on the outside keypad, 01 for apartment 1, 44 for apartment 44. This will then make your entryphone ring, pick up the handset and you should see the people at the front door and be able to talk to them. They will not be able to see you. There is a button on the screen to open the front door for your visitor.