problem with my Samsung Galaxy Y . Help please.

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i purchased samsung galaxy y andriod cell phone few months back. I'm from India. some of my friends said, they got missed calls from me. but i never called them. first i thought they are making fun of me. then i checked their missed call list on their cellphones. my missed calls where there. but i never called them. Can anyone one tell me, how does this happened? i don't use net much on my cell phone, since I'm mostly online on my Laptop or PC. So i don't think its a virus. Help me Please.