I've been a fairly happy user of voice control on my iPhone 3GS and later the iPhone 4. I only use it for making calls, but it's very accurate both holding the phone and via the Bluetooth in the car.
The iPhone 4S will have much more, but I've found Vlingo (http://www.vlingo.com/) and it is better than I thought it might be. You can draft emails and SMS as well as a few other things. It's not perfect, and deeper integration into the system a la the 4S would be better, but it's an acceptable substitute.