In the Windows version of Skype, advertising could appear during free calls between the Skype users.
Skype (owned by Microsoft) has announced that they will be launching a new advertising campaign in their program which at this stage only affects Windows users. This advertising will only appear when free calls are made between Skype users. It will appear in the active window during an audio conversation.
This advertising won’t be present though for users who have Skype credits or service subscriptions. Skype indicates that their advertising will be present in 55 markets where the VoIP service is present, with Microsoft’s advertising service being used.
The advertising will be silent with Skype promising that it won’t change the call quality. It will be executed after the normal checks have taken place like the connection quality.
Skype states that besides normal advertising, targeted ads may be seen depending on the demographic information like location, sex and age. Users can nevertheless refuse this targeted advertising by changing the default Skype options under the privacy settings. If this is done, then only the geographic inform ion will be used for the advertising.
An example of the advertising in a conversation can be seen below:

For earnings, Skype has for a long time called on their subscribers and credit purchases. Advertising started to appear in 2011 via banners on the welcome tab.