I just found this out... for some it may seem like common sense but it was bugging me and I want to let other people know so.... some headphones don't fit into the iphone 2G not because of the size of the plug but because the iphone 2G's headphone port is buried about a centimeter down into the phone (obviously apple didn't want you to use some headphones). But if your favorite pair of headphones has a rubber end surrounding the jack this can be fixed. (I do not guarantee this will work on all headphones) By taking a small blade to the headphones, you can use your favorite pair of earbuds with your phone. All you have to do is shave off the rubber that is preventing the headphone from plugging in. I did this with my noise-eliminating Blockade headphones and it worked like a charm because they had a layer of plastic underneath the rubber so that I didn't cut any important wires, and I understand that most headphones have this. So take out a tiny, dull pocketknife and in five minutes you can be using that expensive pair of headphones!!!!

Picture 1= the purple blotch is where the actual headphone jack starts...the rest is material apple built around the jack
Picture 2= the headphones I used with the part that you want to cut circled in purple...only cut what you need to to make them fit!
Picture 3= my headphones after I cut the rubber off and the chinsy knife I used
Picture 4= zoomed in on the output jack of the headphones after the mod
ENJOY! Hope this helps someone!