Internet sleuths have discovered evidence of a next-generation iPhone in Apple's 2.21 firmware.
Digging through Apple's 2.21 firmware update (which arrived on iTunes earlier this week), the rabid Apple fanboys over at MacRumors discovered mention of an "iPhone 2.1" in the code, seeming indication of a next-generation iPhone.
The "2.1" part is the key indicator here. Apple uses these model numbers to designate different models of hardware, and they typically don't change the first part of the model number unless the hardware features some truly significant hardware changes. Thus, the original iPhone is the 1.1, while the 3G version is the 1.2. The hardware is essentially the same with some changes. In the case of something like the iPod Touch, however, the oldest one was dubbed the "iPod 1.1" and the most recent one the "iPod 2.1." The most recent model added a speaker, volume controls, microphone support and a faster processor, and thus being a significant leap from the original model, warranted the 2.1, or next-generation, label.
If all this is to be believed, we can expect that Apple's next iPhone to step its game up quite a bit. Rumormongers seem convinced that a central part of the upgrade will be the leap to Multi-Core CPUs and possibly GPUs for the phone. More graphical prowess would obviously fit nicely into Apple's plan to make the phone into a viable gaming platform.
Judging from Apple's usual tendencies, MacRumors thinks the phone could see release as soon as June. My first-gen iPhone was looking outdated enough already. Oh well, at least it'll have Peggle.