Difficult to say as Android was Google's answer and a direct response to the iPhone, and may have come significantly later (or not at all) if it wasn't for iPhone.
I think it was only a matter of time. An app market already existed for Palm OS, the technology for touchscreens was there but people were skeptical of giving up the hardware keyboards on their Blackberry, Treo and Sidekick devices. I seem to recall the 3G being where the iPhone really took off, but maybe that's because that's when I noticed my favorite Palm OS developers were all abandoning Palm OS and porting their products to iOS