You'd be surprised at how many people who own iphones own one outside of their means. There are tons of people working two jobs or never eating out just to pay their cell phone bill.
I wouldn't be too surprised. I spent one summer working in a warehouse. Suffice to say the cars (and their respective rims, sound systems, etc) were not within reasonable spending habits for my fellow $8/hr workers. And their families :(
But the point stands: signaling wealth is what counts.
Of course, there are. The question though is whether there is enough of a correlation with third variables to lead one to believe 'possessing iphone' = 'possessing more sex partners' is likely not causal? As GP and other commenters point out, there are enough.
If you're working on minimum wage...yes. That is a fairly significant proportion of their income. 40 x 7.75=$310 (before taxes)=$1240...so $50 is about 4% of their total monthly income, not a small amount to squander.
But the point stands: signaling wealth is what counts.