I-phone apps

As far as I know the I-Phone 3G is using Google maps here in Thailand. Apple is quite restrictive with other maps like garmin and for the time being you will have to make do with Google maps. No local home-brew maps available yet.
 
It seems that TomTom (competitor of Garmin) has made a deal with IPhone as they mention on their website that TomTom will work with the newest IPhones - see http://iphone.tomtom.com/

However, TomTom does not have maps for Thailand nor for most Asian countries so that won't help us much here.