The procedure is simple and easy.
It worked for me.
We are generally not careful while handling the calls.
The cause of the dropped calls and slow download speeds seems to be the location of the antenna.
Gripping the iPhone 4 in the lower left hand corner of the smart phone will cause degradation in the signal and possible signal loss.
The key is to hold the phone in a way that does not cover the black strip in the metal band.
A cheap quick and easy solution is just to put some scotch tape or translucent tape over the two black strips in the metal band so that your hands and skin do not touch it.
This will shield the antenna so that you will not suffer fewer bars or signal loss.