On new iPhone, when I call people no one can hear me but I can hear them I got a new iPhone last weekend and have a problem: why can’t people hear me on the other end of the phone when I call them? Any tips on what the cause could be?
Assuming everything is actually OK with your phone then I had same problem.

I read on another post it is an issue with Apple's attempt at noise cancelation when making calls when background noise is present.  It was suggested to disable noise cancellation by enabling hearing aid mode (under General-->Assesibilty).  They only down side is it makes you enable bluetooth and amplifies your handset volume a bit.  I tested it with several people and they all noted how much better they could hear and understand me.