CIT310 IP w/ Yahoo Voice Phone In calls, can be heard but can't hear caller.

I am trying to let my cell phone forward calls to the Yahoo Phone In service, since there is weak reception at my home. The calls forward and ring correctly, but when I answer it the caller hears me but I do not hear them.

When I have used the phone out service with the phone, it works fine both ways. Can be heard and hear them...unfortunately my main use is for phone in.

PLEASE HELP!!