I have a pair of nice headphones at work. (Sony mdr v6). They sound great and I don't want to replace them. There are 2 things the plug does for me, 1) allows

I have a pair of nice headphones at work. (Sony mdr v6). They sound great and I don't want to replace them. There are 2 things the plug does for me, 1) allows me to easily switch between using my computer for audio or my phone. Prevents my computer from making noise that might bother my officemates (auto play if I forget to turn the volume down) Also isn't there a smaller/thinner 2.5mm headphone jack? I had a phone with headphones for that (Nokia?)