A glitch with the registration software for the iPhone means that many people in the UK are unable to use their devices.
We got the same problem here in NL. But in my case, the registration server was overloaded.
I paid for the black 16 GB version, so they stored it for me. But I need to wait when the systems are back online, so after the activation I can take it with me 
There weren’t many people in the store, so they where attempting to activate it. It took them 5 hours, then they received an email from T-Mobile that they should try it again tomorrow.