To call someone from their own number or any number.

1. Go to http://www.mobivox.com and register there for free account.

2. During registration, remember to insert Victim mobile number in "Phone number
"field as shown below.

3. Complete registration and confirm your email id and then login to your account. 
click on "Direct WebCall".

4. 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.

5. That's it. Your friend will be shocked to see his own number calling him. I have
spent last two days simply playing this cool mobile hack prank.

Note: This trick will only knowledge purpose...
         Just try this trick only known person.