Google shares shave risen almost 20% in the last month

Lehman Brothers said it expected Google to move into the mobile phone market and predicted it could launch its own handset as soon as February 2008.

The shares closed up 0.9% at $615.18 having earlier been up as much as 2%.

Its brief rise above the $620 mark made it one of the 10 most valuable listed US companies for the first time, overtaking Johnson & Johnson.

"We expect the device to be a low-priced, simple-form-factor handset with a Google-designed operating system specifically designed for Internet applications," Lehman said in a note to clients.

It also raised its target for Google shares from $610 to $714.

The suggestion that Google plans to get into mobile phones was supported by the news that it had bought the Finnish firm Jaiku, which makes a mobile phone application that allows people to use instant messaging to keep track of each other's activities.

No financial details of the acquisition were given.

Google went public in August 2004 at a price of $85 a share.

Larry Page and Sergey Brin, who founded the search engine, have seen their wealth rise to $20bn each.

In the past month alone, Google has seen its shares increase 19.6%.