Well, I want to buy an unlocked iPhone 5S at full price, without being binded to a specific carrier. From my understanding I can: A. Purchase online at Apple.com from T-Mobile and get a completely unlocked phone I can use with another carrier. B. Purchase at Verizon store completely unlocked which I can use with another carrier. Correct? Is there any difference between the two? Will buying from Verizon still allow me to use GSM sims (T-Mobile) or are they two different models? (Apple website shows they have four models with different frequencies). Thanks.