WhatsApp Messenger offers you a way to send text messages over 3G or WiFi without paying for SMS charges.
This version of WhatsApp Messenger is designed for Nokia S40 devices, although it's still in beta and currently only runs on the Nokia C3 and X2-01.
In order to use WhatsApp Messenger for S40, you need to make sure that the person you want to send messages to also has WhatsApp installed on their device, though it should work regardless of which operating system they are using.
Configuring and using WhatsApp Messenger is very simple, thanks to a straightforward user interface. The chat window is attractive and permits clear viewing of messages. Features in WhatsApp Messenger are somewhat limited in comparison to other messaging applications, however, and it's lacking tools for group conversations, or file sharing at the moment.
Still, WhatsApp Messenger makes for a great way to save money on SMS charges on your S40 phone.