There are lots of apps for messaging on the iPhone. But WhatsApp Messenger appears to be leading the pack with its simple approach to chat and messaging. There are lots of advantage of being simple: an interface that mimics that of iPhone’s Messages app; there is no login requirement to a chat network; no need to add in contacts as the app uses your existing contacts’ phone numbers. WhatsApp is essentially online chat dressed in a SMS suit, except you do not have to pay for the SMS charges, even for international chat. And the app is available for Android, BlackBerry and Nokia phones as well.