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 set the body in iOS 4. Please cf the documentation.
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];