Best Free VoIP App for Android Phone
Tango seamlessly integrates with devices, always staying on ready to receive (and send) calls. This is a huge plus for people who rely heavily on VoIP calls because it makes it easier to continually receive and send calls. On the downside, however, this means Tango is "always on" -- it uses up battery life even when you aren't actively using it to make or attend calls. For what it is worth, though, during my experience of using it, Tango doesn't use too much battery life. With the amount of how much I use my phone, I typically get four hours of total screen time between charges on my Nexus S. (This gets me through the day.) If I have Tango running, I get 3.5-3.75 hours of total screen time; so Tango makes me lose 15-30 min of total screen time. This isn't too bad if I heavily use Tango because obviously the free calls make up for lost battery life; however it is a waste if I have Tango installed and running but am not using it.

Another upside to Tango's seamless integration is the fact that you don't have to login/logout when you want to use it/not use it. It is always on, as I mentioned. However, on the downside, you are required to register Tango with your cell phone number. While most people will be okay with using their phone number to register (it is for a legitimate reason), some people may not feel comfortable doing so

App Name: Tango Voice & Video Calls
Developer: Tango
Download Size: 4.8 MB
Version Reviewed: v1.6.13322
Requires: Android 2.1 and up