Sorry, i didn't remember that in USA yo cant buy the iPhone free-contract. Here in Spain, for example, if you buy the LC iPhone free-contract, then you can get a 750mb plan for 10$/month. And if you think that the owners of the ipod touch will have a phone too, it's make no sense for me to go for the touch.
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Well, you have the monthly bill of your phone too. As i've said, i didn't remember that you can't buy the iphone free-contract in USA. But, i think that in a near future this will happen, maybe with the LC iPhone? I have to say that i'm a touch fan, i had the 1g for 3 years and now the 4g for another 3 years and i never had the iPhone (due the high monthly bills and free-contract price) but i think that when the LC comes out, (i expect 300-349€ range) the touch won't have sense for me anymore.