Software (not app) To Read Underlying iPhone Data
I don't think there's any software that can do it without jailbreaking the device.

iPhone Explorer is free software for Mac and PC that allows you to browse many files and folders without jailbreaking. If you do jailbreak it is also supposed to let you get at MS messages, call history, etc.

I've not used with with a jailbroken device, but can attest that it works reasonably well in its normal mode (it seems to not work as well with iOS 4.2, though you can still browse and such).