I'm personally banking on the idea that convincing more people to go data-only will be the game-changer. Apps like "Hushed" [1] already wrap phone/sms functionality from Twilio inside an amazing interface where you can pick up numbers anywhere on earth for any period from a week ($3) to a year ($30).

The thought is that when everyone is just seeking out the cheapest data deal, not only does is unbundle and disempower the giant telcos (a good thing), but it also gets users and developers in the mindset of a single data tier. This is where real security and privacy gains can be had.

For example, I've gotten some friends using textsecure, but they've ditched it after being confused why turning off their data prevented them from getting timely sms messages. (Encrypted text messages are silently routed through data when conversation partner has textsecure, even though the identifier seems to be a regular phone number to the user, just like with SMS messages.)

When users start using all-data plans, tools will be developed to help users go into a conservation mode akin to turning off data, just as they do now. Instead of turning off data, users will be able to use a simple firewall to block everything but voip/text messaging apps.

As an added bonus, any trend toward making data-only more convenient will also mean that using wifi-only devices and mobile hotspots will be equally convenient. Those who want the manual baseband separation of that setup (unavailable on current full-featured phones with radios), will not have to jump through crazy hoops to get it, and so security will take a big leap forward :)

/rant

[1]: http://hushed.com/