How to call someone from their own number?
Go to http://www.mobivox.com and register there for free account.
During registration, remember to insert Victim mobile number in "Phone number" field.
Complete registration and confirm your email id and then login to your account. Then click on "Direct WebCall".
You will arrive at page shown below. In "Enter a number" box, select your country and also any mobile number (you can enter yours). Now, simply hit on "Call Now" button to call your friend with his own number.
That's it. Your friend will be shocked to see his own number calling him.