I need to send an SMS from my iphone app. the body of the SMS is created programatically. so when i tap on a button the SMS application should get opened with my message pre-typ
You can't set the SMS body. The only things you can do from your code, as per the official SDK, is 1) to open the SMS application:
NSString *stringURL = @"sms:";
NSURL *url = [NSURL URLWithString:stringURL];
[[UIApplication sharedApplication] openURL:url];
and 2) to set the phone number for a new message:
NSString *stringURL = @"sms:+12345678901";
NSURL *url = [NSURL URLWithString:stringURL];
[[UIApplication sharedApplication] openURL:url];