Skype has announced that the VoIP software can now be used with 50 Java-enabled mobile phones made by Motorola, Nokia, Samsung, and Sony Ericsson.

Users of the phones can now receive calls from the Skype network and to SkypeIn phone numbers on the public switched telephone network (PSTN).

Outgoing calls placed to Skype users and via SkypeOut, its gateway for outbound PSTN calling, will work just in six countries (the UK, Denmark, Estonia, Finland, Poland and Sweden) as well as Rio de Janeiro in Brazil.

This extension of Skype's offering to mobile phones, with calls placed over data networks operated by cellular carriers, is an interesting mix of models. Skype is, on the one hand, challenging operators' high margins in handling voice calls, but, on the other, will require that users of this service have typically expensive data plans over which the calls are placed.

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