The ear buds you get with your mobile don't usually live in the same postcode as audiophile quality headphones, but the built-in microphone can be really handy while on the move.
Thankfully, you don't have to stick with those pack-in buds to keep talking while you're walking. There are headphone adapter cables available that add a mic extension to any headphones you want to use. Belkin sells a Headphone Adapter with Microphone accessory for $24.95 and it is just one example of many on the market.
Before buying, be sure to check the cable will definitely work with your phone.