Method Swizzle on iPhone device

I tried both JRSwizzle, and MethodSwizzle. They compile fine on the simulator but throw a bunch of errors when I try to compile for Device (3.x)

How do we do swizzling on the iPhone? What's the trick?

The CocoaDev wiki has an extensive discussion on method swizzling here. Mike Ash has a relatively simple implementation at the bottom of that page:

#import <objc/runtime.h> 
#import <objc/message.h>
//....

void Swizzle(Class c, SEL origSelector, SEL newSelector)
{
    Method origMethod = class_getInstanceMethod(c, origSelector);
    Method newMethod = class_getInstanceMethod(c, newSelector);
    if(class_addMethod(c, origSelector, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)))
        class_replaceMethod(c, newSelector, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    else
        method_exchangeImplementations(origMethod, newMethod);
}

I have not tested this, simply because I regard method swizzling as an extremely dangerous process and haven't had the need to use it yet.