Are you a T-Mobile customer with an iPhone 6, iPhone 6 Plus, or iPhone SE? You might want to hold off on upgrading to iOS 10 (if you haven’t done so already). It seems a nasty bug is knocking these phones off the carrier’s network, but Apple is reportedly working on a fix.
On March 31 of this year (2016), Apple solved the problem that existed since September of 2014: Power users that wanted an iPhone with the latest CPU but preferred the 4″ form factor could have their cake and eat it, too – again – with the introduction of the iPhone SE. Now, though, that problem starts all over again.