Nokia 5233
Having problem with calls

If I make/receive a call, I can't here any sound from opposite side even ringing tone also.but they can hear me.and one more thing if I keep the phone in loud speaker or if I attached the head set then I can hear clearly.may I know what is the problem I am facing with my phone? can I get it solved? Please help me to solve the problem as early as possible.

Thanks

Sowmya