Simply put: I have an iPhone 6 on AT&T Next 12. My wife only upgrades every two years so she subsidizes through them every two on contract. I've gone back and fourth between annual upgrades and biennial upgrades. I (think) I've done the math correctly, and, since I keep my phone in like new condition I'm best off (financially speaking) keeping the phone for two years, selling it myself at market value, and then upgrading. Can anyone confirm this? All these new plans and options being thrown out from various carriers are dizzying for a guy with a family and a full time job. Thanks for your help. I'm fine with upgrading every two if it's the most economical. It seems (based on sellmymac.com) that the depreciation of an extra year is almost negligible for iPhones at two years of age versus one. I should also note that I do not desire to keep my iPhone beyond two years.