Q: Iphone 4 people cant hear me during calls.

I found that just tapping the phone on something made it work again very consistently.  Nothing else made it work immediately during a call.  Thanks for the tip.

Also, I finally had a chance to get to the Apple store.  They replaced my phone immediately because they said it was still under warranty.  He took offense to my assertion that there was an intermittment flaw in the phone and said it was just my phone despite the fact that he said others had come in with the same problem.  We will see how long this phone lasts.

SOLUTION:

You will have to carry a headphone jack along with you at all times, when your 'out voice' disappears just pop the jack in and out, problem solved until next time

Unfortunately not, it didn't work with the headphone either.   Problem not solved.   It didn't matter whether it was speaker, normal, headset or whatever.  They couldn't hear me until I knocked the phone against something.

My iphone 4 started having this exact same problem less than a week ago. I can hear others fine, but they are unable to hear me. Tried reset, updated to latest software etc, no luck. Just made an appt at genius bar for this Friday. This is a refurbished phone that I have and luckily I have until the end of next month of the 90 day warranty remaining.

Same problem here.   My phone has worked perfect up until about a month ago.  Out of the blue, periodically callers cannot hear me but I can hear them fine.  I tried everything.  The ONLY thing that seems to work is to hit the phone against something and it MAGICALLY begins to work.   Very, very annoying.   It seems like a bigger probelms than Apple is willing to admit.   Unfortunately, my phone is out of its warranty period, so no replacement for me.  

Same problem here...suddenly yesterday nobody can hear me.This stinks; it’s used for my business...now it’s hard to get more work orsupply support to my clients when they can’t hear me. Bumping the phone seemsto work, but it’s temporary and inconvenient. Walking down the street, talkingand bumping my phone every few seconds is not optimal. Apple...what’s thesolution? Are they all breaking? Time for an Android?

I have had the exact same problem and that it seems it happens when the phone is hot ie hot outside or been in a pocket next to your body. The solution I've found is that if i put it in the freezer for a short time it or hold it in front of the air conditioner vent in my truck it starts to work.

Help!  I'm having the exact problem!  I started to notice since last week, but it could be sooner as i rarely talk with my phone! (usually txt and web)  That's really disappointing as this phone is really less than a year old!  All my other phones, from oldies phone to my BB's, they worked for years (and still work if it's activated!) - and they've all been roughed up.  I keep this iPhone like a baby and it's already  broken in less than a year, I expect more from an Apple product.

I'll have to take it to the apple store next when I have time but if anyone knows a fix, please post!

OK...

After three days with the nobody can hear me issue, I headed to the nearest Apple store (40min away). Before I left I checked to make sure the issue still existed...yep. Drive to the store, checked again before I went in and complained...no more problem! Now what? Its been fine for a couple hours now. Is this problem going to return? Probably...right after my warranty is up! Not happy; would have felt better with a replacement, but thats not going to happen if its not broke right now!

You DEFINITELY should have insisted that the problem exists regardless of them being able to reproduce it in-store and demanded a replacement, directing them to this very discussion if they needed any further proof.  I had to do some insisting when I went to my local store but eventually I walked out with a brand new iPhone4 and I've not had the problem since.

Since my last post, my phone was working flawlessly until just now. Back to the nobody can hear me issue. Frustrating...going to head back to the Apple store in the morning. I would really like to know what is causing this.

Latest update:   So from my previous post, my iphone warranty had expired and I took it the Apple store and they basically said, "too bad, I should have bought the extended warranty.  Can we sell you another at full price?".  This was after I had showed them the postings and the quantity of people with the same problem.  Now, this issue is happening more and more  often.   I can't seem to go one call without it happening.  SURE, tapping it on my knee works, but REALLY?   (FYI - Also, I am getting the big I TOLD YOU SO from my Droid coworkers).  

Here's an idea for those who warranty expired.   Most credit cards will extend your warranty for 1 year.  So, I filed a claim on my AMEX.   Waiting on them to respond.  Hopefully, I can atleast get my 300 dollars back and buy a new droid.  

I have to tell you that when I showed the guy at the genius bar the postings and the discussions, he told me they take the forums with a grain of salt, and that they are just user discussions, not confirmed issues. Despite that, they gave me a new one, but I was infuriated and astonished that they would just disregard it completely.  He refused to acknowledge that there was a more general issue.  He would only acknowledge that I there was an issue with my phone.

I ended up taking the drive back to the Apple store afterthis problem reoccurred. The store was very busy, but they were very accommodating.They at first wanted me to wait around for a couple hours until the nextavailable appointment with the genius bar. In the meantime, they had me speakto the "point person" who was more than happy to immediately assistme. I explained the issue and I was asked the normal questions - restore,reinstall, Bluetooth headset (which I do not use). I did tell him that there isa discussion thread concerning this issue, to which he didn’t really seemedconcerned with. He quickly grabbed a new phone and swapped my sim card and activatedthe phone for me. He stated that the "defective" units just go backto corporate for the engineers to dissect. I am happy with that answer as itcould only provide for better hardware with fewer issues in the future. I wishevery manufacturer took that stance on their products! I am happy with the outcome, and I hope this issue doesnt creep up in the future with my replacement phone. Thank you Apple.

you have 1 year warranty in apple, go to the near app store they are will fix it ;D