WhatsApp (Android, iOS, WP7, BlackBerry, Symbian)

A multi - platform application is very popular even in that helps to avoid the payment of fees for sending SMS , MMS as well as NGOs . Truth be told it's a classic client communication for the exchange of messages but who do not require additional registration or manual insertion of contacts into the database .
In a very simple program to use your existing address list ( similar to the way in which Viber works ) and it will detect which users have WhatsApp installed program . Besides sending text messages there is also the possibility of sending multimedia content ( videofajllave , sound recordings and photographs so that it could serve as a substitute for MMS 's) , then in group conversations ( especially the popular thing to those who are barur conversations ) , and even send messages to friends even when they are not online . These messages will show you them when they activate internet connection in their phone .

The only drawback is that after a year of use will be required to pay 2 dollars a year , you can continue to use the service . So the first year is free , the other years , almost free.