I am currently working on a project and am using an old one ear headset with a microphone and 2.5 mm jack. I'm tight on time and limited to radioshack and anything i can find at home. I need to use this on a new smartphone which has a 3.5 mm jack. I couldn't find an adapter in radioshack which i can use. (from my knowledge i believe that in order to have audio and a mic, the jack has to have three rings). I couldn't find any adapters on RS with 3 rings. I was thinking that maybe i could grab a regular jack from RS and just solder it on. But i don't know what jack to use and would appreciate a link to a jack. I'm trying to essentially do whats on here http://www.instructables.com/id/Sony-Headphone-Jack-Replacement-better-and-stron/

 

The plug/jack is called TRS (tip, ring, sleeve). Any decent computer store or office supply store will have a wall of cables and adapters, and probably has either an adapter or a short adapter cable with the genders you want.
Beware that Apple devices and many other tablets and phones use a 4-contact TRRS connector. What you really want is a 2.5 mm TRS to 3.5 mm TRRS adapter. These come standard with many new headsets. At WalMart you probably can get a new stereo headset already wired for your phone (plus a 2.5 mm adapter for older phones) for less than the adapter alone at Staples.

And all of this stuff is on ebay for next to nothing if you can wait.

ak