Was given an Iphone 5s previously used on AT&T, how long will AT&T support the 5s?

What happens when the iPhone 5s reaches software ver.13.00 and can't be updated anymore - will the phone still function?  

Yes. You just won't be able to use any of the new features that iOS 13.x and above has to offer.

@joelandsusan There have been changes since this 3 year old thread was started. An iPhone 5s will no longer work on ATT as of February 2022 when ATT shuts down their 3G network. Not sure what you mean by “reaches iOS 13”, Apple is on iOS 14. The 5s can’t update past iOS 12. That doesn’t mean there are no updates. My old iPad that can’t go past iOS 12 just got an update today to iOS 12.5.3.

@sandblaster I thought the 5S supported GSM/CDMA/LTE (but can't display 4G) and can be updated, if still available, to 12.4.6.

The just of it is the 5S will not work on ATT right now with a new activation and for current customers starting in 2/2022 but if they remove the sim put it in another phone and try to go back it may or may not work.  On prepaid it won't work they are using hard account stops on those. 

@OttoPylot

AT&T 5S was not capable of operating on Sprint or Verizon and had no CDMA support.  It will get updates within ios 12, but not go to 13. 

It is not compatible with AT&T's HD voice and will cease to function (as cellular) next February.   Unlock and sell out if USA

Thanks everyone (@lizdance40 and @GLIMMERMAN76 ) for the clarifications. Looks like my old 5S goes onto the "Apple Display" shelf for display purposes only 😉.

@OttoPylot  I'm sure you have room on your MicroCell closet. 😂

@lizdance40 Funny you should mention that. I am in the process of cleaning them up and getting ready to recycle what I can. Just for fun and games, I reconnected the 154 and it was up and running perfectly in about 8 minutes. I'm gonna keep it online for about a month just to record recent use so AT&T doesn't pull the plug early.