If you squinted hard, the first iPhone was practically a 2001 PowerBook G4 (or a 2000 Power Mac desktop) in a pocket format. The CPU and GPU architectures were different but the performance was roughly the same. On the software side, all the OS underpinnings were carried over from Mac OS X even though the high-level UI framework had been trimmed down and somewhat redesigned for touch.

I wrote thousands of lines of C code on an Atari Portfolio, which was my portable development machine for a few years .. it had Turbo C on it, booted up real fast, and was all I needed to make tweaks in between visiting customers - I wrote database recovery software with it .. It was always very fun to break it out at the conference table upon arrival, make the needed changes (magic numbers), do a quick build and then plop the .com onto the target machine for processing ..

Still have those machines somewhere, great little devices.