I had the same problem and i was disappointed too BUT ... i was so mad that i removed the plastic skin on the face of the screen and guess what ... the voice is loud and clear. Its loud and clear like any other cellphone.
I picked up a 4g iPhone yesterday, and I'm very disappointed in a few things.
1) The ear piece volume is the WORST I'VE HEARD ON ANY CELL PHONE, EVER. This includes phones I had 7-8 years ago. With the volume all the way up, you can barley hear the person on the line. It's actually so bad that the phone is almost un-usable unless you're in a completely silent room.
2) I'm not getting a lot of my texts. I had 2 friends text me 5 times in a row, I never received any of the messages.