if you want to keep the numerical signal strength, just press the sleep wake button until the "slide to power off" appears then press and hold the home button to force quit the application and it will remain on the screen.
Feels as good as "discovering" *#06# on old Nokias!
Does anyone know if this works in the USA? The article is from a domain in Belgium. Plus, any brave Guinea Pigs? I'm reluctant to muck with my iPhone.