Even though WhatsApp, Skype and other apps are mostly used for making international phone calls nowadays, there might still be confusion on the dial codes. Whenever you are using your own US or Canadian cell phone to call a number in the UK, you are making an international call. You will also need to dial accordingly when using Skype.   

• The International Access Code (IAC) for the US and Canada is 011 and for the UK it’s 00
• The Country Code (CC) for the UK is 44 and for the US and Canada it’s 1
• Area Codes in theUK can be various digits in length
• The UK uses a trunk code, it is 0
• To call the UK from the US or Canada, dial IAC + CC + Local Number.

Example: The local telephone number for the National Galleries of Scotland in Edinburgh is (0)131 624 6200. You would dial 011 44 131 624 6200. Notice the Trunk code (0) is dropped when you dial.