Step 1: Buy Some Stuff.
Next we need the Jabra A210s (or any bluetooth to 2.5mm wired adapter). I found these cheap ($20 each) at cell Xpo, link, so I used them over the Cardos, which were about $50.00 each. These will plug into the motorcycle intercom module where the wired headsets would have plugged in. See what we're doing here?
In my intro page, I mentioned that very basic soldering is required, but if you get one of the el cheapo intercom systems and find that the connectors are 2.5mm, you actually wont need to do any soldering at all. Mine is actually different from the ones most commonly found on eBay, and had 3.5mm jacks, so I needed to adapt the 2.5mm jacks to the 3.5mm ones on the intercom.
Lastly, you'll need to buy a couple of standard Bluetooth headsets. If you're in the states you're in luck. Recent legislation in my home state of California has required that anyone using the phone while driving do so with a handsfree kit, which means a bunch of online retailers are making great deals on Bluetooth headsets. I got a two pack on buy.com for $20.00.
Step 2: Pair the Headsets
I also velcroed the entire shebang together for portability (with all the coily wires it looks mighty suspicious - don't try getting this one past airport security.) and put it into a zip-up camera case, then in my bicycle saddle bag or the compartment on my motorcycle to keep it protected.
That's it, please let me know how this instructable works for you, as always vote me up if you liked it, and enjoy!
Step 3: What to Expect / Dealing With Road Noise
This intercom setup will vary greatly depending on the hardware you choose, for example my initial results with a plantronics and LG headset were less than desirable, where the cheapo $20/2pack headsets are quite good. If you look closely in the picture, I've labeled each headset and each adapter with an "R" (rider) and a "P" (passenger). This is helpful for troubleshooting purposes.