Welcome back to the channel—I'm Tony, and in Part 4 of my Grandstream GDS learning journey I walk you through SIP integration that lets an IP phone remotely unlock a door when someone presses the GDS doorbell. I start with the real-world scenario: a visitor hits the green button, the GDS places a SIP call inside your home or office, you vet the visitor, and then you press an unlock option on the phone to release the door. This is a practical way to build a professional-grade access control workflow using standard SIP hardware. I break the setup into two parts: GDS configuration and phone configuration. On the GDS3725, I show where to enter your SIP account details (from your provider or your own PBX), and I call out an optional best practice for businesses—using an allow list so only approved extensions can call the GDS. Then I configure doorbell call routing (the “number called when the doorbell button is pressed”) and enable SIP Open Door with a four-digit unlock code. On the phone side (I’m using a GXV3350 video phone), I add a Door System integration, point it to the GDS extension, and use the same unlock code as the action password. Finally, I demo the full flow—doorbell ringtone, video on-screen, and one-button unlock—plus I explain how it still works on a non-video IP phone.