There is more to this than what the article suggests, at least based on my experience with several different models of iphones and an old speaker phone on my desk.

What I find is that if the iphone is within, say, a few inches of the speaker phone periodically, with the phone not in use and the handset in the cradle, the speaker on the phone makes a sound which clearly is being triggered by something in the iphone (and I repeat this is across several models - original to 5). So it is possible that what is being picked up is the same type of signal that the speaker is picking up but by the part of our body that the phone is right next to.