While still only representing 15% of the total ownership of the iPhone, the 25-50K household income group is experiencing the highest level of growth currently at 48%. The next highest income group growth is at 16% in the 100K+ income range. http://www.itworld.com/personal-tech/57039/low-income-users-latch-iphone
As the article linked suggests this can either mean the smartphone market is increasing its marketshare against traditional cellphones or it could indicate that the Apple Market Fad engine is working really well in that demographic. Either way bringing better communication devices to the lower income crowd should be a good thing for this country.