Try one thing... On your N97 MIni... first deactivate you current whatsapp accouont the uninstall the whatsapp.. then restart your phone and install whatsapp without simcard I mean only on wifi mode.. than insert the sim card other than what you will be using in N9... than try registering with mobile number that you are currently having in your N9 while keeping the sim in N9... you will definately get a message on N9 of verification code.. use that code manually on wazapp and I m sure you will be able to register... let me know the result.. cheers.. sorry for bad enlgish.. try it step by step...