+(UIImage *)makeRoundCornerImage : (UIImage*) img : (int) cornerWidth : (int) cornerHeight
{
UIImage * newImage = nil;

if( nil != img) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
int w = img.size.width;
int h = img.size.height;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);

CGContextBeginPath(context);
CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);
addRoundedRectToPath(context, rect, cornerWidth, cornerHeight);
CGContextClosePath(context);
CGContextClip(context);

CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);

CGImageRef imageMasked = CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);

newImage = [[UIImage imageWithCGImage:imageMasked] retain];
CGImageRelease(imageMasked);
img = newImage;
[newImage release];
[pool release];
}
return img;
}

@end

#import

appIconImage.image = [UIImage imageWithContentsOfFile:@"image.png"];
appIconImage.layer.masksToBounds = YES;
appIconImage.layer.cornerRadius = 10.0;
appIconImage.layer.borderWidth = 1.0;
appIconImage.layer.borderColor = [[UIColor grayColor] CGColor];

i.backgroundColor = [UIColor clearColor];
i.style = [TTShapeStyle styleWithShape:[TTRoundedRectangleShape shapeWithTopLeft:10 topRight:10 bottomRight:10 bottomLeft:10] next:[TTContentStyle styleWithNext:nil]];

#import
…
// Add a corner radius:
CALayer *l = [myImageView layer];
l.masksToBounds = YES;
l.cornerRadius = 10.0;
l.borderWidth = 1.0;
l.borderColor = [[UIColor darkGrayColor] CGColor];

I kid you not. Works like a charm.

Be sure to include the QuartzCore framework, as well as the header up top in your implementation file.