Don't act so surprised. You know the day when a phone will have a quad-core CPU is coming, you just don't know how soon. Well, I believe it's coming earlier than you might expect.
Nvidia talks in their recently released white paper about the importance of multi-core CPU's in smartphones and tablets. The key word here is "multi-core". They are not just saying "dual-core" even though they would've said that and be more accurate. So why didn't they use the "dual-core" word? Because Nvidia has already started that Tegra 3 is almost finished, and Tegra 4 is underway. This means they must be working already on a quad-core chip.
But why go to a quad-core chip at say 1 Ghz, instead of making a dual-core chip at 2 Ghz. The answer should be pretty obvious - energy efficiency. The higher the clock of a CPU, the harder it becomes to increase efficiency of that chip. Basically, the higher you go, the less power per Watt you obtain. Why else would Intel make its most advanced chip yet - the i7 CPU - a quad-core with a 1.6 Ghz clock (sure it can go a bit higher, but that's the standard).
So will we see a quad-core first in Tegra 3 or in Tegra 4? I there is definitely a significant chance we could see it in Tegra 3. We're just not seeing how we can go from 1 Ghz phone in one year, to a dual core 1 Ghz phone in the next year. It's not so hard to imagine we can have a quad-core 1 Ghz phone the year after that. Except I think there will be one major condition for this to happen.
Four cores occupy more space than two cores, so unless Nvidia has already managed to make the chip at a 28 or even 22 nm manufacturing process, instead of the 40 nm manufacturing process that they used for Tegra 2, I don't think we'll see a quad-core for Tegra 3. They will just try to raise the clock speed, optimize the efficiency further, and release it with a dual-core 1.5 Ghz or maybe a bit higher. We already know that Qualcomm will release a dual core 1.5 Ghz chip by the end of the year, so Tegra 3 will at least be competitive with that.
Tegra 4 on the other hand, has a much better chance to receive the quad-core treatment. On a Cortex A9 they can't go further than 2 Ghz, and an improvement from a dual core 1.5 Ghz to a dual core 2 Ghz wouldn't be so big. Plus they'd reach the maximum clock limit of the Cortex A9 chips, so the more obvious route is to go with a quad-core for a significant improvement in performance. They are probably going to make a quad-core Cortex A9 with a clock speed anywhere from 1 Ghz to 1.5 Ghz per core. By then it should also be more than possible to manufacture the Tegra 4 chip at a 28 or 22 nm process.
Whether it will be the Tegra 3 or the Tegra 4 the chip to feature a quad-core Cortex A9 CPU, we will be seeing it in phones and tablets by the end of 2012. The future looks great, doesn't it?