The Nokia 770 Internet tablet, distinctive for being a Nokia device that isn't a phone, has decided to become a phone after all.

Despite coming from the Finnish phone giant, the 770 (reviewed here), launched in 2005, doesn't connect to cellphone networks, and isn't a phone. Now, a software upgrade has changed at least some of that.

The tablet is an 802.11b/g WiFi connected Linux computer, intended for browsing the web, and popular among geeks who like to use it as an open platform to work with.

The new version of the operating system, Internet Tablet OS 2006, includes support for voice over IP (VoIP) and the SIP protocol, so the device should be usable as a phone - at WiFi hotspots.

The OS includes the Google Talk application for voice chat, and making calls to other Google Talk users.

For "real" calls to the PSTN network, a client for the Gizmo Project phone, by SIPPhone will be available shortly, according to Nokia.

The update also improves typing support, with a full touch-screen keyboard. The device's UI has been given a once-over, and it has better memory performance, Nokia says.

For current users, it's a free upgrade, but comes with a warning: "installed applications designed for OS 2005 will not be compatible with OS 2006 edition and will not be restored even from backup."