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I'd use the same stuff you use to clean LCD and plasma screens with honestly...if you must use liquid at all. Rubbing alcohol in my mind isn't very highly recommended.
I have pseronally tested cleaning the iphone with the following products
-windex
-hand sanatizer
-plastic cleaner (used for the iphone demo structures)
i have applied to a cloth as well as directly to the screen, and in no case has there been any deteriation of the product.
the warning i will give, is using items that are corrusive, i.e rubbing alchol and hand sanatize etc... is that if you get it into the phone, it can damage the sensors, so if you need to use that, apply it to a cloth first and use it sparringly.
However, you should never need any cleaning device other than hot breath and a micro fiber cloth, as that has worked for even the stickiest fingerprints. (these att demo phones get some "intresting" people playing with the phone
Rubbing alcohol is relatively harmless to the iphone if used sparingly. It actually cleans better than the cloth alone. Its best feature is that it evaporates almost instantly leaving no streaks.
here are some articles on how rubbing alcohol could actually SAVE your iphone and also how to clean it