Earlier this year, WhatsApp released a web client called WhatsApp Web for Android, Windows Phone and Blackberry. iOS was left out due to Apple platform limitations.
I think WhatsApp worked around the limitations or the limitations have been removed by Apple because WhatsApp Web is now available for iOS users.
Some of you might already know, WhatsApp has been available on Windows MarketPlace For Mobile since last Saturday, but unfortunately, it is only available for Windows Phone 7.5 (Mango) users. Most of us, the “general public” are still on Windows Phone 7.0 and are eagerly waiting to upgrade to Windows Phone 7.5 which I think will be released this week if not the latest next week.