I tried the following solution with the UITextArea and I expect this will work with UIButton as well.
First of all import this in your .m file -
#import <QuartzCore/QuartzCore.h>
and then in your loadView
method add following lines
yourButton.layer.cornerRadius = 10; // this value vary as per your desire
yourButton.clipsToBounds = YES;
~ Answered on 2011-02-21 05:24:56