All five of ours had iPhones for years. We didn't pay a lot for them because we went with a contract. The older kids would upgrade and then pass their older iPhones down to a younger sibling.
Then we discovered the awesomeness of Republic Wireless. My college kids still use their iPhones but they pay for the plans. The rest of us got the MotoX from Reoublic. $25 a month for unlimited talk, text, and data!