The Sprint and Verizon phones have both chips (GSM and CDMA), the AT&T and Telekom phones only have GSM. The majority of the world uses GSM, but some countries only use CDMA. If you travel a lot and want to use local sims while abroad, you better go with a version that allows both.
At least in the US, all phones can/must be unlocked upon your request. However, up until last week (so I learnt in this thread) in order to order one of the phones, you already had to had a contract with on of the carriers. (not for in-store pickup, but, well, stock was and is low...) But, some people are on prepaid and not on contracts.
I ended up reserving mine for pickup as Sprint (with my Sprint account info). I did it on the Apple finance/upgrade plan. But after pickup, took it to AT&T and activated it on their network, using a prepaid plan. And if what u and Apple say is correct... if im unhappy with that plan i can switch to any other carrier...