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It's T-Mobile's Monthly 4G. I've noticed a lot of people hate T-Mobile but I've been quite happy with it; my area actually gets 4G too.

Have fun traveling and having EDGE or GPRS in most places. BTW, that's 3G or Faux G if you wish, but not Four G.
 
I think it would be bad to buy a 3GS. It's rarely good to just go with the cheapest option. It won't be up to date for much longer. Even if you think she won't mind, your sister will want a newer phone. Get the 4. Wait till the next one if you have to.
 
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