Can earphones be paired with two sound-producers at the same time, like the pc and the phone?

This is the essential part of a longer post (soon to be released at
major theatres). 

This relates directly to cell phones. 

So to turn off the built-in PC speakers I disabled them but no sound
comes from the Bose bluetooth hearphones even though they are still
listed as paired with the PC, although the phone also says that the
hearphones are paired with it!!!  

Can they be listed as paired, either on the phone or the PC, but not
really be connected?  Or can speakers or earphones be paired with two
sound-producers at the same time, like the pc and the phone?   Will both
sounds come out at the same time, overlaying each other?      (The phone
isn't making any sound now anyhow, and I don't want to fiddle because
the medical clinic is supposed to call right back.) 


And now I just got bu-dup bu-dap-dup in my ears and I don't know who
sent it or what it means.  Nothing on the PC screen or the phone gives a
clue. I thought maybe the hearphones were turning off but they haven't. 

 the built in speakers are still there and they are now listed as the
default, and now that I got a phone call, removed the hearphones (which
turn themslves off if neither ear has one.)