Historical clue formulations

• Sound around a cradle — 2019-10-12
• Feature of a landline, but not a cellphone — 2016-06-08
• Landline sound — 2013-07-03
• Sound after a hang-up — 2008-09-23
• Indication of service availability — 2005-05-08
• It may follow a click — 2001-09-14