Unable to Register Whatsapp

Hi Everyone,

I recently had to re-download whatsapp on my iphone 4s because of some malfunction. I am currently in London, England, but my apple account registered in the US itunes store. I'm able to download the app, but at one point of the registration process you are told you'll receive an SMS text, or a phone call, to your mobile phone in order to confirm the device. I am not receiving either of these things seeing as I am out of the registered country.. Does anyone know how I can solve this problem and register my whatsapp?

Thanks,

Mike