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I am wondering the same thing since I am on a family plan and both people (including me) have iPhones. Yet, I do not want to pay for the same application twice.

I know that you can share movies and music (if it is on the same computer, but different user). But since the new update did not happen yet (well without manually doing it), I can not try it.
 
The obvious answer is....... YES! Cause.. if you think about it, if you download a song, it's not just for one iPod, you can use it on all the iPods synced with that computer. I'm thinking that is the same with Apps
 
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