T-Mobile Brand different from Sony Brand

Question

Ok the the title might be confusing but, I am curious to know if the Phones we get from our carriers such as T-Mobile are different phones from what actully is made by sony. The reason i say this is that the Box my Xperia Z1s came in was some T-Mobile branded box with Sony Logo etc. Appose to the Nicer boxes that you would get when buying the phone from the manufacture sony
I know that most carriers lock thier phones to their network, but not all phones have a T-Mobile branding permently on the phone.
Does sony lease out the Xperia Design to a company that creates the phones for t-mobile and brands it Sony and T-mobile?
Sometimes i feel really ripped off with the US market for mobile phones, I find that there ARE differences in manufacturing and Technology with alot of the smartphones such as the Samsung Galaxy etc in asia as appose to the USA ( And i do own 3 keitai phones If no one knows what they are, they are Japanese mobile phones. It just seems they build a better product over seas for their own country than they do when they target the Dumb "we buy anything" American market and we get screwd with some watered down version cause you can get away with that here in the USA and no one will think twice.
Anyway does any know if this is true or not?
Sometimes i think the Xperia Z1s should be a better phone. but I love this phone

Answer 1

No, the phones that you get from T-Mobile is made by Sony.  When you purchase the phone directly from Sony, the boxes may be a little nicer that the ones from T-Mobile, but they are the same.  I purchased my Z1 from Sony unlocked and it came in a nice box made of cardboard   Only difference is that the one is unlocked and the other is not (T-Mobile).  Well, the phones may not be locked now because T-Mobile is beginning to sell phones with a unlock code that you can use to unlock the phone one you reach a certain point of owning your phone, if you financed the phone.
Alain Lam