Microsoft has completed its integration of unified communications platform Lync with video conferencing tool Skype.
The move allows more than 5 million Lync enterprise users to connect with over 300 million Skype accounts and vice versa.
In a company blogpost, Microsoft says it will initially allow instant messaging (IM) and audio sessions between users.
To connect the two services, users need to download the latest Skype client and sign in with a Microsoft account or Skype ID. They can then add Lync contacts by using their email address to search, find and add them as a contact before starting a voice call or IM session.
Microsoft made its biggest acquisition to date with Skype, which had a total of 663 million users globally, when it bought the company for $8.5 billion (£5.2 billion) in May 2011.
In a separate company blogpost in February this year, Skype Division at Microsoft President Tony Bates wrote that integrating the service with Lync began the process of what the company calls 'B2X', which "places the focus of business communication on enabling human interactions".
Bates said that B2X looks at communications in a unified way, not as "disparate technology silos focused on one task or protocol".
He added that Microsoft will be adding additional features to Lync over the next 18 months, including embedding enterprise voice support to Lync Online and Office 365 and enabling video connectivity with Skype users.