Snom M10 KLE User Manual page 36

Example - barging in a shared call:
1 Alice is on a call
2 Alice shouts across the room,
"Bob, can you join my call on
line 3?"
3 Bob presses L3 to
barge in the call
Bob is now in a conference call with
Alice and the caller on line 3
Alice's handset
36
Bob's handset