People on the other line canot hear me clear....

I have the iphone 1.0 and i received a new one today and when my friend called me she said she could barley hear me, and that i sounded far away.

so i had my brother call me from my phone to my home phone to hear it for myself, and the same thing i could barley hear my brother and he sounded far away.

I have never had this problem with my iphone before.
Extremely frustrated because i have had alot of problems with the iphone

thanks for your time!