Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Standard headphones have worked for me since the day I got my 3GS. I've also plugged the line-in jack from my car stereo into the 3GS and that works too (though I do have to turn the volume up a bit).
 
Finally, a real answer!

Wow that was tough reading everyone's irrelevant posts. I hate when you go though the time of spelling your problem out and everyone just types without reading your post. Anyhow, I had the same problem. My vibe duos worked perfectly with my 2g iphone, then I upgraded to the 3GS and I had the same problem you are having. I contacted V-Moda and they explained to me about how apple is using the new headphone jack. The 4 pin instead of the 3 pin. It's not apples fault for not making sure that the new phone works with all old 3rd part accessories.
Long story short, tell V-moda's customer support your problem and how you were told that the headphone were compatible with the new iphone which was what they posted on their website. Since then they have removed that statement. Ask for a replacement pair that is compatible with the 3GS and they will have you send in your set for the new model. The new updated model works perfectly.Let me know how everything works out for you.
 
Wow that was tough reading everyone's irrelevant posts. I hate when you go though the time of spelling your problem out and everyone just types without reading your post. Anyhow, I had the same problem. My vibe duos worked perfectly with my 2g iphone, then I upgraded to the 3GS and I had the same problem you are having. I contacted V-Moda and they explained to me about how apple is using the new headphone jack. The 4 pin instead of the 3 pin. It's not apples fault for not making sure that the new phone works with all old 3rd part accessories.
Long story short, tell V-moda's customer support your problem and how you were told that the headphone were compatible with the new iphone which was what they posted on their website. Since then they have removed that statement. Ask for a replacement pair that is compatible with the 3GS and they will have you send in your set for the new model. The new updated model works perfectly.Let me know how everything works out for you.
Thanks for the advice :)
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.