iPhone 3G audio port

Yes, you can. I personally use a 5 year old pair of sony earbuds with mine

well, he's an idiot and doesn't know what he's talking about. you can use just about any headphones that have the standard headphone/microphone plug with the 4 sections of metal seperated by a band of plastic or whatever. apple (thank god) did not use a proprietary connector. i used a pair of blackberry headphones until i realized that the iPhone headphones have a mic button (and my blackberry headphones died).

Agreed.... You can use any headphones

The 3G and 3GS seem different on this point. Though I haven't seen it documented anywhere, with the 3GS holding the switch on the Apple earbuds will activate voice command. If you connect standard external speakers (that are not the 4-conductor connector but are just standard stereo) to the 3GS, the phone seems to repeatedly trigger voice dial. Some of the posts I've seen call this a bug but it would seem that it's not -- if Apple would clarify this feature and emphasize the need to use the appropriate adapter (if that's the answer) I would appreciate it. The 3G (if you mean the actual 3G and not 3GS) doesn't have this feature since it doesn't have native voice command, but I've seen and been told conflicting things as to whether the 3G can accept a standard stereo 3.5 plug. Clarification from Apple as to whether either or both the 3G and 3GS can accept a standard stereo 3.5 connector would help!

somehow, i highly doubt that apple would put a different connector in the GS, simply because of all of the costs that would be involved in a hardware redesign.

if you are activating the voice command with regular speakers, there might be a short in your cable causing this. have you tried it with other sets of speakers?

i've used several sets of regular headphones with my 3g (not gs), and i haven't had any problems. these are regular headphones, not headphones with microphones in them.

i'm also using a set of blackberry headphones with my iPhone right now cause i've had 2 sets of apple headphones break in 3 months, and my blackberry headphones (when i had a blackberry) lasted me a while longer.

I don't think the connectors themselves are different, however the functionality is. The 3GS earbuds have volume up/down and holding the switch activates the 3GS voice command. The 3G does not have these features. My guess is that Apple achieves these functions by shorting or changing the impedance across some of the 4 connectors. The standard stereo plug probably does the same thing, thus the constant triggering of voice command when a standard stereo connector is put in the 3GS jack. But I'm looking for Apple to clarify this. Thanks though.

I have the same problem - once I plug my stereo into the headphone jack, Voice Command starts. That is VERY weird and I hope that Apple will fix this with the next update of iPhone OS!