You could check out the products from LogMeIn, I know they've had Mac/iPhone support for a while... I don't know the extent of it as I don't use iPhone or Mac, but their PC products are VERY good, so you may want to check them out.

They have free versions of their remote access and VPN software for PC, I don't know whether the iPhone app is free or not, what with needing to sell through the iTunes store, but they may very well subsidize it with their commercial products.

Check out these two links:
https://secure.logmein.com/US/products/ignition/iPhone/
https://secure.logmein.com/US/products/free/

Telekinesis can remotely access your Mac through a collection of mini web apps on your iPhone.

Features:

• Stream music and videos from your computer learn how
• Screen capture with mouse click and basic typing support
• Simple iTunes Remote control
• Browse your files
• Run applescript remotely
• iSight image capture
• Basic Spotlight search
• Easily create and add more apps

Security Considerations

• This is still a developer prototype and is intended only as a demo to get people started.
• It will have the same access privileges as your user account
• The login and password you specify will be stored on disk, so should be different, but as strong as your account password.
• Don't leave it running if you aren't using it

Usage

• Run iPhone Remote (Requires OS X 10.4)
• Choose a web login/password
• Open to https://:5010 from your iPhone
• If you want to access your computer from outside of your local network, you may need to configure your router or firewall to support it.

Source