Actually this happened to me this morning,was listening to a podcast as I was walking for exercise.I generally walk 4 miles or more so I know approximately how far and how long it took before I got the message.I had my phone in my jacket pocket because it was snowing out,temps were in the 20's.I was about 30 minutes into my walk when the podcast stopped ,I looked at the screen and seen that familiar temperature icon and warning message.Took the phone out and exposed it to the outside air thinking that it could not get enough air circulation in my pocket.It did not help ,it must have to shut down in a safe mode for a given amount of time ,whatever that is ,either internal temp or combination of time/temp.I got home about 30 minutes later ,plugged it into my charger because I was at 50% before I started my walk ,it now read 42% charge.The screen did not react to my touch swipe for a few minutes,could of been too cold but soon after it worked just fine.Don't have any answers just figured I would post this and read the blogs to see if this was a common issue.Kind of surprised me whenthis happened so I guess I will keep an eye on it for now.