Hi,
I have just buyed a new Smartphone for me in Samsung, "Samsung Galaxy Y Duos S6102". I was just figuring out for a quite few days that how to record the incoming and outgoing calls in this smartphone. As i was receiving some bad calls. I was thinking it to record the call and make it complaint. It's very urgent since my sister is also using my phone only. So, anyone who knows better please inform me as soon as possible.

You can install call recording application from android market , you can try
NG call recorder
and
ACR ie. auto call recorder.