As Mashable reports: http://mashable.com/2009/08/17/tomtom-iphone-2/, Tom Tom is now available for the iPhone in New Zealand, Australia, the United Kingdom, US & Canada and Western Europe.
The is the start of the death knell for dedicated Sat Nav units (aside from possibly those built into cars). Much as the iPhone has integrated music and mobile phones, this app (coming to Android soon, and Nokia already has one) is the first step towards all phones having Sat Nav functionality as standard.
The next, extremely exciting development, will be the integration of Google Streetview into Sat Nav technology – so the maps you are looking at reflect what you are actually looking at (or something). Then from there, Streetview directions beamed onto your windscreen so you have a map/directions overlaid onto your actual view. It’s the future.