As far as Europe is concerned, since Echo has not been officially released other than in the UK and Germany, I think your best choice is to set your Echo with a US Amazon account and link it to a US credit card.
I used my brother's US credit card to test the Amazon Music trial.
I'm in France and I don't buy anything through Echo since some services are not available here.
Some things you can find a workaround (ie "What's the weather like in Paris, France ?" to bypass US regional settings), some others you cannot (ie Voice calls/messaging)