To change your caller identification settings:
To change your caller identification to a previously used Skype Number or mobile number, select the number that you require from the drop-down list displayed and click Save Settings.
If you want to use a new mobile number as your caller identification:
It may take up to 24 hours for your caller identification to be activated. You’ll receive an SMS text message confirming that caller identification is about to be activated.
If the caller identification doesn’t work it might be because it’s not available in your country or it’s not currently supported by the local telecommunication provider for the country you’re calling.
Learn more about the caller identification when using Skype.