void CExampleClass::ConstructL()
      {
      //Scan time for low and high 5 sec, low strength -85, high -70 dBm
      TSignalLevelParams params = { 5e6, 5e6, 85, 70 };

      //
      iGsmHandler = CVccGsmSignalLevelHandler::NewL( *this, params );
      }

  void CExampleClass::StartMonitoringL()
      {
      // Start monitoring gsm signal levels.
      iGsmHandler->StartL();
      }

  void CExampleClass::StopMonitoringL()
      {
      // Stop monitoring.
      iGsmHandler->StopL();
      }

  // Called when signal level changes.
  void CExampleClass::SignalLevelL(
      const CVccSignalLevelHandler* aHandlerInstance,
      TInt32 aSignalStrength,
      TSignalStrengthClass aClass )
      {
      if ( iGsmHandler == aHandlerInstance )
          {
          // GSM signal changed, do whatever is needed
          MakeHandoverDecision( aSignalStrength, aClass );
          }
      }
       

Since

S60 v3.2