Gmail was an already popular concept whose differentiator was a company was willing to set money on fire to have two or three orders of magnitude more storage than their competitor. AFAIK, that's been their only differentiator - free storage space.

iPhone was a breakout product from a decidedly no-longer mega corp who practically died in the 1990s. I guess they had already made a resurgence with the iPod, but I think iPod leading to iPhone is similar enough that it's the same jump.

A mobile app from a company is a breakthrough product in your eyes?