Symbol 5506 from IEC 60417 - Title/Meaning: Enquiry call Function/description: To identify the control which allows the use to ""hold"" someone talking, whilst making another call.
Additional information: 
See ITU-T Recommendation E.121
Published in: Supplement J, 1990
Own work using: iso.org/obp/graphics/grs/ac10420b-a910-4856-94c9-8fff7030e44f 200.png
Vectorization:  Mrmw