I have the wifi 3G one.

The issue is that as its registered in the US, I can't buy books on the UK Amazon site. Was hoping that I could as there are some not available here that I would like. They also have different free books at times.

Evidently you can only buy kindle books in your country of residence Amazon site.

I have found that I would have to change the country and address associated with my Kindle in the Manage your Kindle section to be able to do this.

I do use both sites lately but have yet to be able to complete a kindle purchase due to the restrictions which is annoying at times.