Steal this idea: Off-hold notification

Woke up this morning I was all alone

Saw your picture by the telephone

I was missing you oh so bad

Wish I had you here to hold

All I've got is this touch-tone phone

So I guess I'll give you a call

-- Telephone Song (Stevie Ray Vaughan)

Here's another app idea for smart phone software developers. When I'm put on hold and I don't have a headset, I'd like to put the phone down until I am taken off of hold. I'd like it so that when the phone "hears" a loud signal over the line (it may need to do some noise cancellation in case there is noise on my end) the phone will vibrate or (optionally) switch to speakerphone.

This would mostly be for talking to people but a harder problem is handling customer service centers. (Ideally, customer service telephone systems would take your phone number and have an agent give you a call when they're free rather than wasting time on phone calls, but few companies do this currently) In these cases, it might be able to use a voice/music detector and check for repeated messages. Many of things you hear while you're on hold alternate between music and voice, so this might end up notifying you too much. With luck, it could be trained that some pieces were recordings (by memorizing sound "fingerprints" or something like that like) for use in later phone calls.