...in the US. Mexico didn't get iPods that year. Mexico didn't even get the first version of the iPhone when it came out. You had to buy it in the US and unlock it. I think the first iPhone legally available in Mexico was the 3G.
8000 BC - 1998: no "i" branding.
1999: Apple release the first in a string of hit products under the "i" branding.
early 2000's to present: many other technology companies and products use "i" branding.
2004: in a completely unrelated development, a Mexican company names itself iFone.
I guess the "i" branding is a natural extension of "e" branding that followed from email. Anyway like I said I dont think Apple should have exclusive rights to "i" branding for various reasons, the biggest of which is that it doesn't seem like they've attempted to defend it against hundreds of other products using it.