Megapixels don't mean jack. The sensor is what actually matters. Stop focusing on numbers.
Megapixels don't determine quality, and at today's levels I agree that they "don't mean jack" for cameras with optical zoom, but for a phone camera they do matter. If one can't get close enough to a subject, such that zoom is needed to get a decent shot, then the only option on today's iPhones is to zoom digitally. On today's iPhone 4, trying to emulate a 3x optical zoom involves zooming into the middle 1/9th of the image which, for a 5MP sensor, is the equivalent of a 0.55MP sensor for the zoomed-in area of the photo.
With today's technologies, boosting megapixels for a given sensor size reduces quality significantly, so I'm not advocating huge MP sensors because the quality would then be rubbish for all photos but I'm saying that, if aliens were to land and deliver Apple an unlimited supply of 45MP sensors at the same quality as the iPhone 4's 5MP sensor, it would actually be useful to have in the iPhone 5 because it would then be possible to have a decent quality zoom function in a mobile phone camera which would make it a more viable replacement for a regular compact camera.
I saw an article somewhere about some research project with concave sensors where the curvature of the sensor itself was being varied to give genuine optical zoom within a much thinner unit that a traditional telescoping lens arrangement so if that ever makes it out of the labs then that is another alternative for getting genuinely useable zoom options into the thickness of a mobile phone.
If the sensor quality is good then I'm perfectly happy with 2MP photos for my holiday snaps with maybe 3MP as a high end luxury version so, to get a digital equivalent of a 3x optical zoom on a 2MP camera needs a raw resolution of 18MP and for my 3MP luxury option it's 27MP. The technology is nowhere near that yet but, for the reasons I gave above, I can see a use for high quality sensors of that resolution in a camera unless/until concave variable geometry sensors come along and solve the problem or some fieldishly clever retracting lens assembly that can retract fully into the iPhone 4 body when not in use can be created.
- Julian