Vodafone has acquired a Danish mobile startup called ZYB for 31.5 million euros ($48.7 million).

ZYB combines a back-up service for your mobile contact and calendar info with social networking tools that allow you to share the info with your friends. Its service also allows you to send images and messages from your computer to multiple mobile devices.

Now, there are plenty of mobile social networks out there, and web heavyweights Facebook and MySpace also have mobile sites. But as others have noted, ZYB has been smart in the way it has grown from a back-up service into something approaching a full social network.

Vodafone says its larger strategy is to grow revenues through fixed broadband services, mobile advertising and integrated mobile/PC Internet services, so it’s easy to see where ZYB fits in. The startup will remain in Denmark and become a part of Vodafone’s Internet Services division.

ZYB chief executive Tommy Ahlers says ZYB will remain free to everyone, even if they’re not Vodafone customers.

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