For Blackberry devices with older versions having keyboard they just need to press the space bar. Nokia Symbian users hold the center button to record the message. Leaving these buttons will automatically send the message to recipient.
Press the "end call" buttons for cancelling a msg on Blackberry and Symbian devices.
When the Microphone icon next to the message turns blue it means the message has been listened or heard.
So Update your Whatsapp Messenger Now and Talk to your friends Via voice chat