Microsoft plans to launch the final version of its Windows Live Messenger software on Tuesday.

The application replaces the company's MSN Messenger product which has about 240 million users, according to company data.

The new version adds support for voice calls between a PC and a regular telephone number as well as voice calls between PCs.

Windows Live Messenger's voice calling features were pioneered by Skype, which boasts over 100 million unique registered users.

Both services require users to deposit funds into an account which is billed for used calling time.

Skype dropped fees for calls within the US and Canada in May, but is still charging for calls outside those regions. 

A first version of Windows Live Messenger was released in December to a limited group of testers, and has been available as a public beta since May.

The release marks the first core application under the Windows Live brand to leave the testing phase.

Microsoft unveiled its Live Software strategy last November. It is set to further expand over time to cover about 20 online applications including email and blogging services. 

The online services initiative is an attempt by Microsoft to better compete with Google as well as to increase its overall revenues from online advertising.

The free Windows Live Messenger will be available for download from Microsoft's Windows Live Messenger website.