Nokia has updated the operating system for its Wi-Fi Internet tablet device, adding support for voice-over-IP and instant messaging, the company said on Tuesday.

The new version of the software for Nokia's 770 tablet supports SIP-based voice over IP (VOIP) clients and comes preinstalled with Google Talk. The operating system, based on Linux, also supports IM clients based on Jabber, an open source instant messaging platform.

The software includes a full-screen keyboard that users can type on with their fingers, and Google comes as the default search provider on the device.

Nokia said it added the new features based on customer feedback. The number-one request was for VOIP support, followed by requests for IM and better input methods, Ari Virtanen, vice president of convergence products for Nokia, said at the VON Europe conference in Stockholm.

The new operating system will become available during the third quarter.

Nokia introduced the Nokia 770 last year. It ran on a Nokia implementation of the Linux tablet operating system. While Nokia has said that the device is selling well, it has also refused to give sales figures. The device has features similar to recently launched products based on Microsoft's Origami design but costs about a third of the price.

In a departure for Nokia, which is best known for developing products for the cellular industry, Nokia 770 doesn't come with built-in cellular support. Instead, it has Wi-Fi, although users can connect their cell phones via Bluetooth to use a cellular network to reach the Internet. "Users are likely to prefer a high-speed LAN," Virtanen said.

The addition of Wi-Fi to Nokia devices has been met with mixed reactions from operators, said Mikko Salminen, director of marketing for fixed-mobile convergence at Nokia. Some cellular operators see Wi-Fi as an opportunity to sell more cellular access, while others see it as a threat, he said.

Nokia's E series phones, announced last year and geared toward business users, include Wi-Fi and cellular and have been eagerly awaited by the market. Jeff Pulver, founder and chairman of Pulvermedia, the organisation that puts on the VON conferences, said he bought an E61 at a shop in Stockholm Monday and was told the phones had just arrived at the store the day before.

Earlier this year, Nokia said the phones would hit the market during the second quarter but wouldn't ship in volume until the third quarter.