Whats App (whatever that uses?)
Whats App uses the Whats App service. Whats App is an IM service for iPhone and iPod Touch users only. Whats App is similar to the Blackberry IM service which is for Blackberry users only, but Whats App is provided by a 3rd party and not by Apple.
There are 3rd party IM clients at the App Store that bring most of the major IM services that are available together under one application.
With the Beejive IM app, the following services are supported and all can be available and logged in at the same time if you have an account with each service.
AIM/MobileMe
Google Talk
ICQ
Jabber
MSN/Windows Live
Myspace IM
Yahoo Messenger
Facebook IM
However, I would pay for apps which consolidate IM services. I would pay up to £40 for an app which enabled IM on my iPhone to talk to the Blackberry Chat IM users.
Since it is RIM - the Blackberry manufacturer and the party that provides the Blackberry IM app for Blackberry users only, you need to contact RIM with your request since it is RIM's responsibility to provide an IM app for the iPhone and iPod Touch to be compatible with the Blackberry IM app which is for Blackberry users only.