I have iPhone 3GS with iOS5 installed.While making SIP calls through Fring, Skype, Nimbuzz or Nymgo using WiFi internet, I am unable to hear audio through built-in ear-piece of iPhone but instead works fine by attaching Ear-phone or Headphone. Pls help?

Dear Friends,

I have iPhone 3GS with iOS 5.1 installed. While making SIP calls through Fring, Skype, Nymgo or Nimbuzz VOIP applications using a home WiFi internet, I am unable to hear audio through built-in ear-piece of my iPhone but instead it works fine by attaching external Earphone or Headphone through the socket in the phone. Can anyone help me rectify this problem so that I can make SIP phone calls using above apps in a normal phone conversations mode, without having to attach external ear-phones? Thanks.Sudhir