Im tethered on 4.2.1 on a iPhone 4, been about a month, running flawless. had to reboot once I think when installing MyWi, Used to worry i'd crash at work or something and be out a phone all day, but its been perfect... almost forgot I was tethered...Like its been said here before, dont Reboot - Power Off - or run out of Battery unless you have a computer and cable near by..