Whatsapp Messenger, the name like words daily people says “whats up dude?”..:-D, prety cool name. Actually this is a messenger application for smartphone and according to the official Whatsapp site, it’s support for iPhone, Android, Blackberry and beta version for Nokia symbian OS.
According to the official WhatsApp site (again), this app was developed by two guys who spent combined 20 years doing geeky stuff at Yahoo! Inc. before starting WhatsApp Inc. Below the link to download Whatsapp for free 1 year trial, after the trial period you can purchase service for US $1.99 / year.
Not all type can use for this WhatsApp messenger, there are several smartphone list supported for WhatsApp and minimum system OS requirement for WhatsApp.