Currently Being ModeratedNov 21, 2013 3:30 AM (in response to lilangi)
There is no stand alone officially unlocked iPhone 5S available in the US, at the present time. So, in that respect, the genius is correct. However, the T-Moble labeled iPhone 5S, if purchased directly from Apple, is in fact officially unlocked, and will work/activate on any supported GSM carrier, anywhere in the world.
Be aware, a US iPhone's warranty/support is only valid in the US, & the phone will not support LTE anywhere other than North America.