To answer the OP's question, "how do families afford these smartphones?"....my answer is the same way they afford all the other "toys" that people now think they "need".
My thoughts here are not an indictment of what choices other families make, as long as they can afford those choices for the long term and their families thrive. But for my family, we have learned to say no to most of the things others think they need. Many folks choose to have gadgets, but don't have nearly enough in the bank/investments/under the pillow to for retirement or to take care of themselves if they lose a job. Many folks are in debt up to their eyeballs. For many people a major car repair is a deal breaker and causes a panic. Unexpected illness wipes them out....and that's not just a major illness like cancer. And lots of 2-parent working families.
Our consumer oriented population has a serious streak of entitlement going on. Everyone "needs" a data plan. Has to have cable TV and a flat screen high def huge screen to go with it. Ipods, Ipads, etc, etc, etc.
My kids think we are poor. My DS15 is dying for an Iphone/data plan. We only have enough cable so we can get maybe 10 channels...pretty much what we could get with an antenna in the old days. Off-brand MP3 players (except DS who has an Itouch has a bday gift from grandma), 10 year old TV that will stay until it dies. Our cell phones are around $130 per month on a family plan that includes 2 grandparents. Get a discount through DH work. Oh, I do spring for Hulu streaming only. Only debt is our house payment, but we will probably end up with a car note soon as both of ours are around 100K miles and one is 11 years old. One vehicle is a mini-van, the other a Pontiac g-6. No sport utes.
But we do have retirement funded, some money for college, a stash in case of an emergency. My kids have taken some fun trips. We do not panic about money...just worry about how to prioritize it some times.
Again, these are choices my family has made...I have no problem with anyone making whatever choices works for them as long as they can pay their bills, both today and later. Just don't live a lifestyle that means you'll need help living when you retire and make you can cover routine unexpected expenses. I don't want to hear you whine on facebook about money woes while you are posting from the grocery store on your smart phone!
Sorry about the rant....this question obviously hit a hot button for me. Guess I am tired of being responsible!