For comms in a motorcycle helmet, look at CEP. You won't have to install earphones, just the CEP jack, and the CEP will provide the audio. You will have to add a microphone, and that can be a little tricky, but with the proper parts, it's not too difficult. You'll need a boom, a mike, and an attachment fitting, along with a 4-conductor cord and a plug, and wires in the helmet to get everything to the right place.
I use CEP in my SPH5, and wouldn't be without them. You can find them at
this site.