There are a couple of issues going on here. Let me try to unpack them...
First, you can reduce the amount of radiation your body receives from your iPhone by keeping your iPhone away from your body. The radiation isn't technically avoided, but it is reduced by the square of the distance. So using earbuds will help to the extent that they allow you to keep the iPhone physically away from you.
Of course, if use the earbuds to keep the iPhone in your pocket, then your body is still getting the same level of radiation... it's just going to the middle of your body rather than your head.
Second, there's the larger issue of whether or not the radiation emitted by your iPhone--even when held to your ear--is harmful in the first place. I'm in the camp that says it isn't.
After all, you get exposed to a certain level of radiation all the time, every day. Eating a banana exposes you to radiation, for cryin-out-loud. So does sleeping next to someone in bed or walking by a granite building. (Source) So obviously we humans can handle a bit of radiation without too much trouble.
- Jeff