Symbol 5507 from IEC 60417 - Title/Meaning: Call waiting Function/description: To identify the control which activates a signal to inform the user that someone else is trying to reach this telephone during communication with another party.
Additional information: 
See ITU-T Recommendation E.121
Published in: Supplement J, 1990
Own work using: iso.org/obp/graphics/grs/287ead2b-de7d-4ebe-90cb-43e5d08b113b 200.png
Vectorization:  Mrmw