...

1. Use Call Park feature via 3CX

(1) Login 3CX system ? → Setting ? → Call Parking ? → Get "the Call park place number"
e.g.: SP10

(2) Login IP Phone A's webpage ? → Function Keys ? → Line Key/ Memory Key ? → Set Type to "Call park", fill "SP10" in the Value field


Login IP Phone B's webpage ? → Function Keys ? → Line Key/ Memory Key ? → Set Type to "Call park", fill "SP10" in the Value field


(3) C calls A, A answers, then A presses the Call park key, C will be held.
(4) B presses the Call Park key, then B will talk with C.

2. Use Call Park feature via MyPBX

(1) Login MyPBX system ? → PBX ? → Basic Settings ? → Feature Codes ? → Call Parking Preferences ? → Get "the Call park feature code"
e.g.: *6

(2) Login IP Phone A's webpage ? → Function Keys ? → Line Key/ Memory Key ? → Set Type to "DTMF", fill "*6" in the Value field


(3) B calls A, A answers. A presses the DTMF key, then A will hear a voice prompt about parking position (The parking position is usually "690") and hang up. B will be held.
(4) C calls "690", then C will talk with B.
PS:
Call park LED:

...