Go to www.cellity.com but If you have received an invitation but open the link you were sent and download Cellity on your mobile. After launching the application just follow the prompts and you'll receive an activation code by sms. If you are using JAVA MIDP-2.0 handsets (eg: Nokia S40 series), exit the application, check the code, launch the application again and follow the prompts to activate it. But if you are using NOKIA Symbian handset, activation will be automatic.
Things to remember:
--You can only send free sms from cellity to cellity user (anywhere in the world). Cellity user is any one who has the application installed on his mobile.
--To invite people to cellity send them an sms using the application. Don't bother to write a long message, it won't show your sms to the receipt unless he/she has the app. installed
--When you are offline, you'll receive a call from number +496966102800 which you won't be able to take (it's just a flash/beep) notifying you that you have a new sms.