HP have used a combined Mic-in & Headphone-out socket on their Laptops and Netbooks for many years now.
See the discussion here http://h30434.www3.hp.com/t5/Notebook-PC-Sound-and-Audio/HP-Mini-210-Netbook-Headset-Audio-Combi-Socket-Port/td-p/309235
... and the adapter cable available from eBay for 99p linky'ed on the fourth page of thar thread.