You don't even need to disconnect the ear bud, just tap it. The voltage pulse from an audio signal is sufficient. Back in the days of rotary phones I used to show off how to dial numbers by simply tapping the receiver on the table.
That doesn't seem to work - I have a POTS line here, and no amount of tapping or striking the phone receiver on a surface is the equivalent of dialing (I tried the phone itself and my headset microphone). Perhaps a local VoIP ATA works that way, but my Telco does not. And I'm not surprised, there's a big difference between detecting an audio signal and detecting a local loop interruption through 18,000 feet of copper.
Perhaps so in some countries, but in the USA, pulse dialing still works (even VoIP ATA's here support it). There's lots of older automated equipment out there that depends on it (elevator call boxes, alarm systems, building front door call boxes, etc.)
My "in case of power failure" phone is an old red Bell System desk phone with rotary dial. Still works great.
