Internet voice services provider Vivox has been around since 2005, but it’s been focusing on building partnerships with game developers lately. Now, the Natick, Mass. company has just closed a $6.8 million third round of funding to “accelerate its growth;” IDG Ventures led and Benchmark Capital, Canaan Partners and GrandBanks Capital participated.

Today, it says it has 20 million total users in 180 countries, with clients from Second Life creator Linden Labs to Electronic Arts (full list of companies and games, here). Its services let developers integrate voice features in a variety of environments, from directional sounds that let players hear things like footsteps behind them to virtual goods where users can buy upgrades to get new kinds of voices like a monster or an elf. It also offers audio ads. It makes money from licensing or revenue share deals from these features.

Voice is an inherently social service. Although it hasn’t been a key part of big social games, Vivox may help change that.

The company has raised $21 million total to date.