I can hear people, but they cant hear me on my iphone 4

Hello...
Few days back i bought my iphone 4 mobile phone. But i am having a problem related to the volume while calling any person.. No-one can hear me on the phone. Doesn't matter if they call me or i call them, sometimes people can hear me and other times they can't, or it cuts out half way through a problem. Is this problem fixable. Any help would be greatly appreciated.. :)
Please find some solutions as i am not able to talk to anyone i call...

If this happens all the time, then the problem is definately with your microphone. I have used two iPhone 3Gs so far (one was returned for some hanging problem), and I haven't had any problems with the other phone related to caller hearing me. It works fine and i can hear clear sound of the opponent who is talking to me on the phone.

I am not sure that what it is. I've been meaning to sort it out, but it started happening for me when I upgraded to the latest firmware. Basically it works fine for about 4 to 5 minutes and after that they cant hear me anymore, like the audio qualtiy gets worse and worse until nothing. I am not at all happy with it as i cant do anything without my cell phone.. It will not work on any calls after that, until I reboot my phone again...If you have any other solutions please post it...

I saw many posts on internet for solving my problem. I then decided to have my iphone upgraded with the latest software. I received an Upgrade Request when I went to iTunes and synced some stuff. The microphone now seems to be working fine.. I dont face any such problems now as i have upgraded my iphone with the latest software.. I hope this information will help you solve your queries.
Any help would be gratefully received.

Hey i had the same problem with my iphone where someone would call or i would make a call and after about 2 minutes they wouldnt be able to hear me.
I tried restoring all the settings but nothing worked.. I finally tried taking off the vibrate mode when the phone rings and also going to carrier settings - network selection - i changed this to o2. Then i changed it back to automatic..
Now the phone calls work perfectly again.I am not sure if this is definitely the solution for this but its something you people can try.It worked for me. Atleast try this out...

I just fixed my microphone... It was going in and out for a few days where I could hear but no one could hear me. All I did was i just tighten the 2 screws at the bottom of the phone. They were loose but did not look loose.. I have dropped my phone many times and I attributed it to a loose connection!
And i am happy that this thing actually solved my problem. I hope this solution proves to be useful to you guys....

I had the same problem with my iphone until I realised I was covering the microphone with the tip of my finger while making a call... The best way to test it, is to make a call using the speakerphone make sure that you keep fingers away from the bottom of your iPhone. Else you can go for the service at the apple service center...

Past 3 weeks i can hear people but they cant hear me when i speak, if they do hear me after a minute they cant hear me. I restart the phone and still same problem. It randomly works when it wants. Not sure if its my network or my phone Im sure its my phone. I dont know what to do. Its frustrating.