I have a "tuneups Skullcandy LINK" cable setup that works with headphones/earcovers that is part of a Giro Fuse model ski helmet. This worked beautifully with an iPod and my old Verizon phone. A two-ring 2.5 mm male plug plugs into the right earcover/headphone/speaker of the helmet. About nine inches later, there is a thumb sized clip with a single large button (that you can push with a gloved hand) that will cause the phone to answer when pushed; also has a volume wheel, and a built-in mike. Then there is a considerable length of wire that at its end, splits into a 3.5mm male 2-ring plug that you can plug into an iPhone or iPod to listen (only) with. Now, here is the important part -- the other end of the wire went to a 2.5mm male 3-ring plug. This plugged into a variety of cellphone model adapter cables. My original adapter cable for an old Verizon phone was a female receptacle that received the aforementioned 2.5 mm male plug and a 2.5 mm male plug that was plugged into my old Verizon cellphone. With this set-up, you could easily receive a call by pushing the big button on the thumb-sized clip, talk into the mike on the clip, and listen through the headphones/earcovers in the helmet, all with your cellphone safely tucked away in an inside zipper pocket of your ski jacket. I thought it would be easy to purchase an adapter cable with a 3.5 mm plug for my iPhone. Our local Apple store said they used to carry them, but no longer; but they sent me to Frys. Frys told me they used to carry such an adapter cable (3-ring male plug 3.5 mm), but no longer because customers reported that although the plugs mechanically interfaced just fine, the set-up didn’t work - couldn’t hear and the mike did not work.
On a lark, I purchased a “2.5mm to 3.5mm Stereo Audio Headset Adapter for Apple iPhone/ iPhone 3GS - Switch any Music Phone Stereo Handsfree with 2.5mm 3 ring Plug to Apple iPhone Stereo Handsfree” (from Amazon for about $1 + $4 shipping); the picture clearly showed a 3.5 mm 3-ring male plug. At first, I disconnected the old Verizon adapter cable and plugged the new plug from Amazon in. I was disappointed that that did not work at all. As a last ditch effort, I lugged the old 2.5 mm cable for my old Verizon phone back in, which then was plugged into the new cable from Amazon, and voilà, plugging that into my iPhone 3G, now I had the sound from the iPhone (either the iPod music or iPhone incoming sound) and the outgoing voice from the clip-on mike, and the ability to answer an incoming call just by pushing the big button on the clip, just like I had before with my old Verizon phone. So basically, identical set-up, with just one more 4.5 inch long adapter cable. This works beautifully, and only cost me $5.
There are more elegant wireless solutions, but a quick search of CNET showed they were expensive and the quality for cell phone use not all that great (worked fine with iPod functionality). I’m not sure if Giro just makes a more modern wired (& cheaper??) solution for the iPhone. My setup (the original for the Verizon phone) is a few years old now.
