I'm in a long-distance relationship, and sometimes when I'm talking with my girlfriend, I talk her to sleep (through a bedtime story, I mean, not by being boring...) - the problem is that after she's drifted off to sleep, and I'm smiling happily and end the call, the dialtone noise of the phone wakes
her up again.
So I thought, what if phones are designed so that you can press a button during the call to select 'silent ending'. Then if the other person hangs up, your phone makes no 'brrr' noise.
This might not work for normal phones for two reasons:
a) the earpiece might burn out if left off-hook too long (but maybe not, it's not producing any noise so shouldn't be using much energy)
b) since it's not replaced on the hook, the phone would still be engaged if someone else calls, and most people would probably prefer to be contactable in case of emergency
However, it should be straightforward to make a speakerphone work this way - since they can be switched off by the touch of a button anyhow, silently switching it off when the call has ended should be pretty do-able.
An alternative method if the phone can't automatically sense when calls have ended would be to have a 'sleep' switch which switches the phone off silently if you have been silent for 15 minutes.
Okay, so it's probably only couples living far apart (and perhaps parents separated from their children) who might have a use for this function, but think of how happy they'll be to drift asleep blissfully to the sound of their lover's voice without a 'brrrurrrring' phone interrupting their slumber...