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The original iPhone did not usher in the era of the 2.5 mm audio jack.

That's because it didn't have a 2.5mm audio jack. How can it usher in the era of something it isn't a part of?

I believe that weird Motorola iTunes phone had 2.5mm

I believe the very first batch of the first generation did... I know someone who got one very early on and complained about it.

It did not. You might be thinking of the fact that the headphone jack was recessed in a way that caused many 3.5mm headphone plugs not to fit:

Ah, that sounds like a reasonable explanation.