I received my US$5.85 Speaker-Mic from DealExtreme (referral).
It works fine.
You have to remove the rubber cover (and screw) to make room for it to plug it. Put those in a safe place in case you wish to reinstall them later.
The microphone body includes an earphone jack of 1/8-inch (3.5mm) diameter, but it is mono (for a mono earphone, not for 'walkman' headphones with a stereo connector).