Simply you try this:
#import <QuartzCore/QuartzCore.h> //in header file
myButton.layer.cornerRadius = 8;
OR you can do this:
If you want a circular button than create an image with a circular shape filled with whatever you want to be displayed in the circle. Make sure your image has an alpha channel and delete all the area around your circle so the background of your image is transparent (alpha =0). (http://www.gimp.org/ is free and easy to use application for such images)
In IB create a round rect button with type custom button. Select your image as the background of your button and there you have it.