Users of Skype can download the Skype Web Toolbar. The Skype Web Toolbar recognizes phone numbers and Skype Names on webpages, so that you can call with one click, through Skype. It works well when using Salesforce.com. No Salesforce.com configuration required. All phone number fields are transformed into clickable links that launch Skype to dial that number.
This will work well for non-US users too. The toolbar allows you to select your default country so that a country code is not used when dialing.
The Skype Web Toolbar is available for both IE & Firefox.