Before the iPhone was released, the mobile web was a mixture of rudimentary WAP/WML, or if you were lucky awful browsers that tried to render HTML. Everybody hated it.
Then the iPhone was released and it had a web browser in the same ballpark as real desktop browsers. What's more, WebKit was open-source. In next to no time, all the major phone vendors had a WebKit-based browser of their own and the mobile web took off.
Yes, if Apple didn't release the iPhone, eventually we would have gotten decent mobile web browsers. But phone vendors were doing an awful job of it up until Apple moved the whole industry forward. The only other possibility would have been Opera, but that would have required unrealistic licensing deals to have the same impact as the iPhone, and Opera ended up switching to WebKit too.
You're also forgetting about the effect the App Store had on the mobile marketplace. Before the iPhone, buying a mobile application tended to be something that nobody did. Every app had to roll their own payment infrastructure – it was painful for developers to charge and it was painful for customers to pay. Then the App Store came along and made it easy. There was little movement on centralising this beforehand from any other vendor, but as soon as Apple did it, everybody else hopped on the bandwagon.
Yeah, that was my thought exactly. However, iPhone software was so radically different from everything else at the time that I still wonder "what" it would have been and what the App Store revolution would have looked like.
Of course, in this alternate universe it's just as likely that other amazing advancements happened because Apple didn't do iPhone.
3G wasn't the deciding factor, the first iPhone didn't have it but responsive sites started popping up right away. There's also no point in 3G for web browsing unless you have a decent rendering engine – WML and XHTML Basic sites were hardly data hogs.
I am far from Apple fan boy and never actually owned any of their products, but boy they really brought mobile revolution to this world. It took competition many years to catch up with that, with great help of Google and their Android. Main reason why their share price skyrocketed during that time.
I bet that nothing much different, another company would have made one in 1-2 years timeframe. The idea of "hand phone-computer" was very old (decades in sci-fi and real products in nineties called "PDA"). It just happened that around the time when Apple made the first iPhone, tech was advanced and cheap enough for the mass market. To sum up, it was perfect timing, not revolutionary idea.