Thank you Alli for fixing the title. I apologize but I am at work and was in a hurry. You see, i am currently using the Incredible, but I am having signal reception problems where I work. A few friends with VZW iPhone seem to get much better reception. If I can determine that for sure, I may switch myself to the iPhone.
There is a Debug Console option for the iPhone and iPad but it is for Debugging websites in Safari. It doesn't fulfill the purpose you are looking for but in case others are searching for this purpose and find your #1 google listing (as I did originally) I'll post it here:
Home screen > Settings > scroll down to the third section and select Safari > then scroll to the bottom and select Advanced > then turn on the Debug Console.
Now when you view websites, errors and hints will be listed. Great for mobile developers or any normal user with too much time on their hands.
Dial this on the iPhone 4, and it will go into Field Test mode. Up can see the true signal strength in the corner where the bars normally are. -116 would be no bars, whereas -47( I believe it is) would be full signal.