I graduated HS in 2014. By the time the 4s came out they were pretty ubiquitous. Carrier subsidy existed to make one or two year old iPhones pretty cheap (I vaguely remember iPhone 4 being 'free' from verizon for a while). I didn't get one until after many of my peers (iPhone 5 era), but I had an iPod touch and a phone with a full keyboard which was a common combo among the people I knew who were later adopters of smartphones.