i am using sip, so I was just making the configuration. It was successful, but I cannot listen to the caller.

If I call with another mobile to my Sip Number, then I can here the ringing, but I cannot hear any sound of the caller, actually nothing.

If I call from another Sip number to my Sip number, then I can here everything.

So, I think there is a problem in configuration. Any ides?