Microsoft having to lower prices is more a function of the total cost of a PC these days. When an average PC cost $2000, suddenly $200 for an OS upgrade wasn't huge. Now when your PC costs $100-$200 then a $200 OS upgrade suddenly hurts the pocket.

Also for Microsoft's strategy to succeed its essential for them to get as much of their market using Windows 8 and Metro as quickly as possible. Hence the sacrifice of the existing cash cow in the hope it will birth a new cash cow.

Microsoft has redesigned Windows and lowered prices multiple times in the past, before the advent of the iPhone. I wouldn't call this a disruption. Furthermore, I would guess only extremely few people are choosing an iPhone rather than a laptop/desktop computer.

Microsoft redesigned Windows around tablet interfaces and launched their own ARM hardware to run it.

How much does it take before you'll call it a disruption?

I was specifically talking about the iPhone. Tablets definitely stand a better chance at "disrupting" the industry although this is also debatable.

I will call it a disruption when people start using iPhones/iPad instead of laptops/desktops. This doesn't seem to be the case for a large majority of people.

It's not necessary for it to be a majority to be a market disruption.