Skype - With the Skype app, you can make free Skype-to-Skype calls, and send and receive IMs for free, one-to-one or with a group. You can also call phones at Skype’s great rates – over WiFi or 3G.
To make calls to phones abroad, simply dial the number in Skype and pay with Skype Credit – or make unlimited calls with a subscription
fringAndroidVersion: 22.214.171.124 updated Upload Date: 1 Mar 14
fring gives you FREE Video Calls, voice calls & chat to friends over 3G and WiFi (Video calls only on capable devices).
Communicate with friends in the fring network and other supported services: MSN Messenger, GTalk, Twitter, SIP, Yahoo!, AIM & ICQ
GroupMeAndroidVersion: 4.2.9 updated Upload Date: 30 Dec 13
Start a group, add your friends, and we’ll give you a free phone number for it. GroupMe is the easiest way to start conversations and keep in touch with your real life network. It's totally free, and it works on every phone
MobileVOIPAndroidVersion: 4.01 updated Upload Date: 14 Jun 13
MobileVOIP - With MobileVoip you can make free* voip calls from your mobile phone. Make calls to any country you desire at the cheapest rates. MobileVoip is currently supported on iPhones, Android phones and Symbian phones. Simply download the free MobileVoip app from one uour APP market and register with one of the supported Voip brands
IMSDroid is the first fully featured open source SIP/IMS client for Android. It is also the only free Android SIP client which supports direct Video Calls.
3GPP IMS (IP Multimedia Subsystem) is the next generation network for delivering IP multimedia services. IMS is standardized by the 3rd Generation Partnership Project (3GPP)