The inability for people to read the documentation and do the tiniest modicum of research before posting questions on here is growing very wearisome...
I searched in google for calendar in iPhone SDK but i found about Google Calendar or No API for Calendar available.
Really? A search for "iphone calendar api" turned up plenty of relevant results for me.
yes.
http://www.google.co.in/search?hl=en&q=Calendar+API+++iPhone+SDK&aq=f&aqi=&aql=&oq=&gs_rfai=
this is what i searched.
7th result.
Still, do you only ever try one set of search terms in Google then give up?