Mumble is a voip service with very low latency allowing several persons to talk with little to no lag, regardless of connection. You can view all Mumble's code repositories here. Also make sure to check out the Mumble wiki for more advanced settings and options not listed in the above video overview, which can be found at their FAQ
Direct download links for Mumble 1.2.3a:
Download for any device using iOS (iPad/iPhone/iPod/etc) from the iTunes App Store
Anyone who is afraid to click links from a website feel free to go to Mumble's official website @ http://mumble.sourceforge.net/. The links to install the program are on the main page.