if your taking over your mates contract you dont need a new sim at all, you just transfer your number to his contract, continue using his sim in his phone, as for all the data, phone numbers etc, just back up your old phone onto your mac, then wipe the new phone and plug it into your computer and restore it as your 3g, this will transfer all your numbers, settings, email accounts and even photos and texts from your old mobile.
if your taking over your mates contract you dont need a new sim at all, you just transfer your number to his contract, continue using his sim in his phone, as for all the data, phone numbers etc, just back up your old phone onto your mac, then wipe the new phone and plug it into your computer and restore it as your 3g, this will transfer all your numbers, settings, email accounts and even photos and texts from your old mobile.