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if it's not jailbroken probably not through USB, but through wifi yes, try wifi HD, just to name one, there are definitely more out there.
 
'Air Sharing' is another one that I've tried and it works well. In order to use it your iPhone (or iPod Touch) has to be connected to your network with the app running, but once you do that the iPhone acts just like a network drive. The really cool thing is that you can then browse the files on your iPhone, even if you're not connected to the network at the time, and any file that can be interpreted by the iPhone (e. g. AAC, MP3, PDF, Word, Excel, iWork, etc, etc) is viewable on it.
 
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