For those unfamiliar, Whatsapp is an application that can be found on iOS, Android, Blackberry and even on several Nokia devices. It basically allows iOS users to communicate with their friends on other platforms for free, which kind of defeated the whole point of having BBM which was limited to just Blackberry owners, and we’re guessing that not many people enjoy juggling multiple applications for texting either and given the number of platforms being used at the moment, it just makes sense to use one that would be able to communicate with the majority of them.
If you’ve noticed, Windows Phone 7 is not one of the platforms supported by Whatsapp and we’re guessing it has something to do with the very small share of the smartphone market that WP7 commands, unlike iOS, Android and RIM which are currently top three. However it appears that a recent job posting from Whatsapp has asked for people with strong programming/debugging skills in C/C++, and given that Windows Phone 7 is coded in C# it could very well mean that Whatsapp could be coming to WP7 handsets in the future.
For those on the fence about which platform to go for, at least one of your problems could be solved if Whatsapp does indeed come to WP7.