I reworked the project to make it run on iOS 4+. It works with iOS 6. Correct callout bubble style with iOS7.
I changed the project structure, because it was a bit messy and add a namespace to the lib.
This project was taken from this address: http://blog.asolutions.com/2010/09/building-custom-map-annotation-callouts-part-1/
Unfortunately, this blog seems to be offline. Since the code was pretty helpful to me, I decided to upload it again over here. You'll also find a pdf with the original post.
I have no relation with asolutions.com whatsoever. It seems that the original code has no copyright yet so feel free to use it as you want.