Actually you buy the i-phone from 3, that much easier from online shipping. But you need to take the 3 plan.
You need to unlock the I-phone by yourself. The 3 wont help you to unlock it.
If you get a account from itunes store, so that you can dl the stuff from itune. You dont have to buy it from 3, because the online shipping's I-phone also can do that. The itunes store has everything, dictionary games programes, you can download it from there.