Anyone know of a way or a service to control a Mac over the internet?
Really depends on what you need the Mac to do. One of the cooler things I've seen Mail do is run AppleScripts based on the message contents, etc. You can always run a web server and feed it commands back to do various things as well. If you don't know want to script anything, Automator can do some of the heavy lifting for you.
I'd imagine even if VNC or remote desktop worked on the iPhone, you'd be scrolling around and double-tapping quite a bit just to control the Mac. It'd be tiresome pretty quick I think.