... how long would you let it ring?

I just read about the Oxford Electric Bell which has been ringing away since 1840.
It's has been left in a corridor in the Clarendon Laboratory at the University of Oxford.
It was set up by Reverend Robert Walker, who is not taking calls right now, about 176 years ago.
Fortunately, it has been placed behind two layers of glass, so it isn't bothering anyone any more.

.Scott said:

I just read about the Oxford Electric Bell which has been ringing away since 1840.
...
It was set up by Reverend Robert Walker, who is not taking calls right now, about 176 years ago.

186 years ago.

renormalize said:

186 years ago.

You must be exagerating!

DaveC426913 said:

Just imagine the poor guy on the other end of that...

"Your call is important to us. You are 13,437th in line. For your listening pleasure, here is Dan Emmett's 'Dixie' on today's Top Hits..."

Perhaps that is what inspired the introduction of the "Penny Postage Stamp" in the UK - as an alternative to getting a message out.