Can I use What's App on iPhone with no data plan?

I have been using What's App on my iPhone 4 in California for a couple of years now. But when I moved overseas last year, I cancelled my phone plan & have continued using What's App when I'm connected to Wi-Fi.

However, it suddenly wouldn't connect today (Just kept saying "connecting…"). I deleted the app & re-downloaded it. But now it won't even accept my phone number. Just keeps saying "Could not connect to WhatsApp service. Please try again later." The Wi-Fi is working perfectly for my other apps… What is going on?!

Whatsapp said they are having problems today.

Dude, do you live in a hole? Facebook just bought whatsapp for $5 billion, they're switching everything