I have an iPhone 3Gs with Rogers and I pay good money to use their service.

BUT- A friend of mine got a jailbroken iPhone 3G and updated via iTunes to 3.1 not knowing any better. I wanted to try and fix it for him and I just read on Gizmodo that they've cracked 3.1 if you're using a Mac. I have a Mac but will I mess something up with my iTunes and my legit iPhone/syncing, etc if I try and use my computer to unlock his phone?

thanks

If you are "unlocking" his phone you wouldn't be using iTunes.