uInternationalTelephoneInput

That International Telephone Input Jquery Plugin for International Telephone Input with flags as an Umbraco 7 Property Editor:

More details here:

http://www.tooorangey.co.uk/posts/that-international-telephone-input-umbraco-7-property-editor/

The excellant jquery plugin that this property editor uses is here:

https://github.com/Bluefieldscom/intl-tel-input

(including plugin option details.)

The Google Telephone Number Validation library is here:

https://code.google.com/p/libphonenumber/

You can configure defaultCountry etc by passing a json object as as a prevalue for the property editor eg: {defaultCountry: "gb"} would set uk telephone number to be the default format selected. 

You may also want to use

{preferredCountries: ["gb", "dk", "us"]} to promote countries above the alphabetical order.

The editor doesn't prevent the telephone number from being saved if it is invalid, just gives you a visual indication whether google thinks the number is valid for the selected country.