>WhatsApp is a lot bigger overseas than it is in the US (largely because it's a free alternative to SMS in countries where SMS carries significant charges).

Not nitpicking here, just genuinely curious. What do they charge in US for sms? Here the cheapest package i suppose would be 20,000 SMS per month for $1 per month. I normally use the 1200 SMS per week for 10 cents per week though, as my usage isn't that much.