After my iPhone 3g's (not even 3G S) last update, it became noticeably slower. It became one of the main reasons I upgraded my phone. It never spontaneously rebooted, but it
definitely became
slow.
I ended up getting a Samsung Galaxy S5 in 2015. I've replaced the battery once after the original started swelling, and it's still going strong. I plan to next upgrade my phone in 2018/9. I'd be pissed if the OS updated and suddenly made it very slow before then!
