1.Nimbuzz.com
The Nimbuzz app works with both smartphones and feature phones. They even have a desktop client for Windows and Mac. First time users need to sign up for a free Nimbuzz account after which you can start adding people to your contacts. It offers free Nimbuzz to Nimbuzz voice calls over Wi-Fi or 3G and also works as an IM integrator — you can sign in to Google Talk, Yahoo chat, MSN Messenger & Facebook accounts to chat with your friends and share photos. You can also have a group chat or create/join chat rooms
2.OoVoo.com
ooVoo offers free 12way video calls from a computer, mobile or a browser window. You can send files, record calls if required and even create a private (password protected) video chat room.
3.Rocketalk.com
You can't have a conversation or do a video chat over Rocketalk but you can use it to send free photos, videos and text messages to anyone who uses Rocketalk. It's available for Android and as a Java app which works with almost every feature phone around.
4.Skype.com
Skype hardly needs an introduction. You know that all Skype to Skype calls are free, but you can also keep Skype running on your phone (Android, iOS, Windows Phone, Symbian) & make free phone calls to any Skype mobile user in the world (over 3G or WiFi).
5.Tango.me
Tango is a free video & phone call service for Windows PCs and smartphones running Android, iOS and Windows Phone. It scans through your contact list and automatically finds and adds people you can 'Tango' with.
6.Viber.com
Viber is available free for Android, iOS, Windows Phone and BlackBerry. As long as you get the person on the other end (wherever they may be) to install Viber on their handset, you can make free unlimited phone calls and send unlimited text messages. It works over both 3G and Wi-Fi, so the only cost you really pay is for data. The great thing with Viber is that there are no ads and you don't need to sign up — your phone number is your identity. Just make sure your friend's number is in your phonebook.
7.VoxOx.com
You can get VoxOx for iOS, PC or Mac. All communication within the VoxOx network is free (even from phone to phone) but you can also send large files up to 100MB. Upload a file and a short URL can be shared in a chat.
8.Fring.com
Fring offers free voice calls, video calls and instant messaging over 3G or Wi-Fi. It also offers 4-way group video chat for free. The app is available for iOS, Android and Symbian phones. You need to sign up for a free account after which you can add other people with their Fring username.
