Take the 2-minute tour ×  my girlfriend is currently using an
iPhone 3G (iOS version 3.1.3 - 7E18) and I've noticed it can be
very sluggish. She doesn't use it for much more than the usual
messaging/safari/mail. Compared to my 3GS it is pretty terrible.
I used to have a 3G (still do in fact, and it runs much
smoother/faster).  So my question is, what is the best version
of iOS to run on an iPhone 3G?  I'm going to downgrade (if
necessary, which I think might require jailbreak which I'm not
thrilled about) or try a restore and see if that fixes it, but
I'm not sure if it's even possible to restore her phone but keep
it running 3.1.3.  Any advice would be greatly appreciated,
thanks!  share|improve this question Let's see if I get this
right. You're talking about 2 iPhones 3G and 1 3GS, right? And
you only said the iOS installed in one of them, and that's the
3.1.3 running slow. So you're thinking in downgrading it to
below 3.1.3? If so, why not making it the same iOS it's running
good at the 2nd 3G? –  Cawas