If deference to an older post by j7469, as of Beta 7 the old Nokia alpha string *3001#12345#* now launches a Field Test app on my iPhone 4. 
How I discovered the app's presence, I was having problems with making a call with my ATTWS iP4 one night, but picked up my VZW phone in error to check what was going on with nearby towers and was surprised to see 1xEV-DO and 1x menus.
FYI, don't get frustrated with the menus, tapping on the arrow/caret on the right side of the screen works, sometimes tapping on the characters doesn't work. And, the app button quits the Field Test app without issue - the Ec/No number (signal strength) don't "stick" when quitting the Field Test app. If someone else posted this elsewhere, forgive me - I did search first before creating this thread.
How I discovered the app's presence, I was having problems with making a call with my ATTWS iP4 one night, but picked up my VZW phone in error to check what was going on with nearby towers and was surprised to see 1xEV-DO and 1x menus.
FYI, don't get frustrated with the menus, tapping on the arrow/caret on the right side of the screen works, sometimes tapping on the characters doesn't work. And, the app button quits the Field Test app without issue - the Ec/No number (signal strength) don't "stick" when quitting the Field Test app. If someone else posted this elsewhere, forgive me - I did search first before creating this thread.
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