Browsers in other phones sucked. I'd owned high-end "smart" phones before the first iPhone and ultimately went back to a flip phone because they just weren't worth using. Usability of the first iPhone browser was a huge leap forward.
Ironically, that was largely because it let you more easily use sites built for desktop, due to the larger screen space and ease of pinch to zoom. Those older phones would have been somewhat more useful if mobile first/responsive sites had been a thing then, but it took the popularity of the iPhone for that to happen.
At the time you pretty much had palm and wince and feature phones. Of the three wince was probably the better of the interfaces (but that was a mater of taste). Data was expensive to buy on most carriers. Which all the other carriers mimicked within a couple of months of iPhone coming out. The iPhone was decently better than the other two and the 'unlimited data plan' and the bling bling of 'apple'. Also the browser being worth anything. The built in ones for all the others were junk.
Then people started sideloading and basically showed Apple they needed a store which they quickly came up with. Getting an application on the other two platforms at the time was mind numbingly bad (activesync was to put it mildly awful to use). In some cases you needed to get the carrier involved (better have a few months to validate and a few hundred thousand dollars to pay for it).
Also that screen they used was way better than what any other phone out there had at the time. Most of the top end phones needed a stylus and itty bitty keyboard to be any sort of useful.
I would say it was not until the droidx came out that anyone had anything that approached how cool the iphone was.
Mobile browsers were a painful experience before that.
Mobile keyboards were a painful experience before that.
I think Blackberry was the only one that did both OK enough to take seriously. I know people loved the Sidekick, but I never used it and don't recall if people used a web browser on it, or just text messaging.
The first iPhone was more impressive than a Blackberry.
Most feature phone browsers were very limited compared to what Safari supported (almost the full web experience at the time). You'd have to look at other "smartphone" class devices for something comparable, and those were not common (EDIT: among consumers) in the US at the time.
Ironically, that was largely because it let you more easily use sites built for desktop, due to the larger screen space and ease of pinch to zoom. Those older phones would have been somewhat more useful if mobile first/responsive sites had been a thing then, but it took the popularity of the iPhone for that to happen.