Dialog-Info Call Pickup

[Yealink Support]

I think you can enable "Visual and Audio Alert for BLF Pickup". This feature should be supported by SIP server.

Enter the webpage->Phone->Features->Call Pickup, enable Visual Alert for BLF Pickup.
The visual and audio alert for BLF pickup features allow the supervisor’s phone to play
an alert tone and display a visual prompt (e.g. "6001<-6002", 6001 is the monitored
extension) when the monitored user receives an incoming call. The visual alert for BLF
pickup feature also enables the supervisor to pick up the incoming call of the monitored
user by pressing the Pickup soft key directly.