Why is a calendar entry made for each call?

I use a Samsung Galaxy Note. I am noticing that each time I make, receive or miss a call, an entry is made in My Calendar, with the details of the call, incoming or outgoing, phone number etc. Every call made / received in the phone log has one calendar entry, making the calendar totally unusable. I am not able to find which application is doing this. Is there any way I can stop this entry from being made for each call? Alternatively, how do I identify which application is making this entry, by looking at the calendar entry?