Free iSMS Free-iSMS is an iPhone-style sms chat software for S60 3rd&5th
WhatsApp Messenger WhatsApp Messengeris a messaging app which allows you to exchange messages with your contacts without having to pay for SMS
Skype (Symbian) Make calls and chat for free, whenever you have a WiFi or 3G connection
IM+ Talk IM+ Talk for symbian 5th edition such as Nokia 5800 or N97 allows you can chat with Skype friends, call any PC, mobile phone, making it very cost effective and it does not need WiFi and works on all carriers networks as well
uTalk Universal network communication chat center with file transfer ability, location service and much more to explore!