Quote from Ivanfrost:
how do i know what part is in my phone? There are 2...
Once you have the phone apart and have gently unplugged the power ribbon, read the part number on the ribbon. If it's in the 821- family, you can safely use corresponding 821 headphone assembly. If it is the other part number, use the newer replacement. Many sites list both parts and let you order the appropriately numbered part. Otherwise (if you order the wrong part) it won't work or you'll have to [unnecessarily] hack the part to get it to work.