So the processors on the devices are not fully exploited, but with overclocking it is very much possible, but only on jailbroken iPhone/ iPod touch. The processor of the iPhone 2G, 3G is indeed 600MHz, but Apple has underclocked it to 412 MHz only, iPhone 3GS instead of 833 MHz it is operated at 600Mhz. But its easy to run them at their factory clocks.
How to Overclock CPU on iPhone 2G, iPhone 3G, iPhone 3GS, iPod Touch
Step 1. Make sure you have a Jailbroken iPhone/iPod Touch. (Jailbreaking guides)
Step 2. Using a SSH tool like Filezilla, Navigate to System/Library/System/System Configuration/PowerManagement.bundle/
Step 3. Rename file “com.apple.SystemPowerProfileDefault.plist” to “SystemPowerProfileDefaultbak.plist” or something that device doesn’t recognize.
Step 4. Reboot, and your iPhone/iPod Touch would Run on native Processor clocks.
Important: Increasing the clock speed would degrade the CPU’s lifespan by several minutes. However, since the device is not designed to handle the heat generated at higher clocks, we recommend you to terminate apps if device appears to overheat. Also checkout tips to Prevent Overheating of iPhone