Vivox has figured out something good: gamers like to chat. The gamer voice chat company is announcing today that it had 45 million users in 2010, up 150 percent from 18.5 million at the end of 2009.

While voice chat companies may seem old hat, the Vivox success shows that focusing on a passionate group of users and serving them well has its rewards.

Gamers use Vivox to chat with each other over the internet while playing online games such as World of Tanks, a popular new online World War II tank battle game. In fact, the gamers now chat for 3 billion minutes a month.

The numbers grew fast in 2010 because Vivox was integrated into a number of games from companies such as Wargaming.net, IMVU, Runewalker Entertainment and Bigpoint.com. The companies integrate the voice chat so that users can all talk to each other on a kind of party line and plan their strategies together. To do that, gamers need a high-quality solution and they don’t really want to download a separate application, said Monty Sharma, vice president of product management and marketing at Vivox. He said the company is adding new users at a rate of 2.5 million a month.

Sharma predicted the company could grow at least 100 percent in 2011. Much of the growth this year could come from Sony PlayStation 3 players, Sharma said. One of the most recent popular games to use it is DC Universe Online.

The trend is being validated around the web. When Google Voice integrated with Gmail, it processed 10 million calls in its first week, said Rob Seaver, chief executive of Vivox. Vivox makes money through audio advertising and virtual goods offers. Other partners using Vivox include Sony Online Entertainment, CCP Games, Linden Lab, and Nexon.

Natick, Mass.-based Vivox has raised $21 million in three rounds from investors including IDG Ventures, Benchmark Capital, Canaan Partners and GrandBanks Capital. Vivox has 38 employees. Rivals include Dolby, Skype, Teamspeak and Ventrilo.