OkCupid's latest update gives useful advice for folks taking pictures for their online dating ads. In short, use an SLR instead of a point-and-shoot or (worse) camera phone, use a short focal range (F stop of 1.2 is best), don't use a flash, and take the picture in the afternoon. But they give all kinds of cool crunchy data making the case.
But most folks will look first to the stats on "number of sexual partners by type of smart phone", which is all about selection issues and very likely has very little to do with the effect of the phone. In short, iPhone users have twice as many partners as Android users. But if you're the kind of person who prefers an Android to an iPhone - and I have indeed been thinking about an Android should I ever find a bit of spare cash - then getting the iPhone instead would be very unlikely to help you much. The single among you may do well to keep an eye out for those iPhone users.
I'm an Android kinda guy who is, as yet, too cheap to get an Android.