They'll probably try to make it so that WiFi must always be on. Then again, it'll have to be locked on the device, so it wouldn't be very hard to get pass it once the phone was rooted (the devices will run Android [according to the article]).

Then, they would probably check to see who was using the majority of minutes/data on Sprint, and then have a talk with them (or throttle their data).

I'm curious as to what they would do with people who sign up and don't live in cities. If you live in rural areas, it's doubtful you'll have WiFi the majority of places you go. They would probably end up losing money on rural subscribers, then try to make profits from urban subscribers.

There might be a problem with a strategy like that though, because it doesn't seem their profit margins would be too high. I'm not sure how much it costs them to buy data in bulk from Sprint, but doing unlimited data for $19 isn't going to result in amazing profit margins. I'm also assuming that they won't be buying voice minutes, because if these devices can use multiple networks, the only way to keep a single phone number would be using VoIP. Of course, there's no way they would be buying text messages, because text messages can easily be sent over e-mail.