for those who bought 5S full price when it first came out, how did you unlock it?

I am seriously thinking of buying iPhone 6 without contract (full price).

I understand that when the iPhone 5 or 5S came out first, Apple did not offer the full unlocked version until several months later. I understand several people bought it full price.

So I am curious, when you bought a full price iPhone 5S when it first comes out (within the first month), how did you get it unlock? Will AT&T (or T Mobile) unlock it for me without question if I provide proof of purchase (copy or fax)?

Thanks.

source: forums.imore.com