All below application works only if you have good internet connection in your Android mobile phone.
WhatsApp Messenger – Cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS.
Viber : Free Calls & Messages – Call and text anyone, anywhere. Viber lets everyone in the world connect. Freely.
Facebook Messenger – Chat with your fb friends,with all popular feature like Text ,Group conversation,Notification.
Skype – For free IM & video calls from your mobile phone.
eBuddy Messenger – Chat on multiple MSN, Facebook, Yahoo, AIM, ICQ, GTalk, MySpace & Hyves accounts ,Chat everywhere with eBuddy Messenger.
Bluetooth File Transfer – Allow You to share more files and formats audio, video an image, you can compress .Zip, .GZip and .Tar files.
Iphone user can also get all above application in Apple iphone store.