Ask HN: Business model of sites like GroupMe?

What is the business model of sites like GroupMe? How are they planning to make money? And how scalable is it?

They are provisioning a new number for every Group. Twilio charges half a dollar for a phone number if you buy more than 1000 numbers. Plus they are spending money on text messages and conference calls. All of this is free for users.

How long will their 10 million dollars last? Or are they waiting for someone with deep pockets to buy them?