UK phone number locator to check if it belongs Jersey, Isle of Man, Guernsey or the UK etc.
UK (+44) Telephone code-number locator
My favorite sim and VoIP for roaming in Europe and worldwide:
UWT-mobile and Xxsim: for call+sms in Europa extern and Worldwide
ToggleMobile: for internet+call+sms only in EU intern
(VoIP/Sip) FriendCaller or SipCall.ch: Worldwide sms+call