Bebo, which recently usurped MySpace as the UK's leading social networking site, will also allow its users to integrate with Windows Live Contacts.
The integration will enable all 36 million Bebo users worldwide who use Windows Live Messenger to display their Messenger presence with their Bebo friends directly on the Bebo service.
Equally, the partnership offers Bebo the opportunity to grow its network through the Windows Live Messenger user base.
Windows Live Messenger is used in more than 60 countries by more than 280 million active users each month.
The Windows Live Contacts API allows users the ability to freely import and export their contacts and relationships between the two services.
Bebo users with Windows Live Messenger will add an "IM Me" icon which will appear on their profile page. In displaying their presence, all Bebo users - regardless of whether they have a Windows Live ID or not - will be able to begin an IM conversation with each other.
Bebo had 10.7 million unique UK users in July.