I know this thread might be very old.
But, for you developers that wants to load annotations from a property list (.plist) file, this CodeCanyon item might interest you:
Mobile - MyPlistMap for iPhone & iPad - CodeCanyon
Your .plist file is downloaded on your server remotely, and you don't even have to update your application in order to add more pins.
Moreover, this Xcode project is also fetching the annotations on your server to a Table View, so that your users can switch from Map mode & List mode.
I'm sorry for this advertisement, but I sincerely hoping this item will be saving you from some painful hours of coding

!