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If you're jailbroken, you could type "sysctl -a" in mobileterminal, and it'll display the clock speed on one of the lines. It is indeed 600MHz. My 1G iPod Touch says 412MHz, and my 2G iPod Touch says 532MHz. Both of those have been confirmed, so I'm pretty sure the 3G is indeed running at 600.
 
It's 600 and ram is 256....stop asking questions that has been posted all over the web...if you want to know for sure...take the dam phone apart...You'll have your answer for sure...no more doubts that way.....zzzzz
 
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