Talking problems with samsung blackjack II? Please read and help.?

I have a samsung blackjack II, it's been working fine, i just got it like a month ago. I didint do anything or change anything to it, but the problem is when people call me, or i call them, i can hear them perfectly and fine, but they can barely hear me like, they cant even hear me. I diidnt change anything in my setting, is there something i can do?