Some BlueTooth headsets, like this one by Helium, allow you to connect to your computer and cell phone simultaneously. You'll be able to listen to music until a call comes in, and stop the music when you've got an incoming call.
Your laptop will need to support BlueTooth for this to work, though. If it doesn't, you can get a USB BlueTooth adapter to provide this functionality.
Hope that helps!
Unfortunately, I haven't messed around with this kind of setup to answer any of those specific questions -- hopefully someone else on the forums here will be able to fill in some of my blanks and even correct me if I'm wrong.
I assume those aren't the only Bluetooth headphones with that capability -- they're admittedly the first ones I found that mentioned working as described when paired with both devices simultaneously. You'll definitely need a headset if you're going to want to make phone calls, as basic headphones won't have a microphone to speak with. I assume that when you finish with a cell call, you'll be able to resume listening to your music without too much hassle, but, again, I've never actually had the opportunity to try it myself.
