[dragonwriter]

> Apple and WinPhone do this fine and it's an excellent idea in a world where SMS is overpriced that the app should automatically look for free ways to get the message to the target seamlessly.

Smartphone plans with unlimited text and limited data with a high surchage for overages are easier to find than ones with limited SMS and unlimited data, so its not really clear that "SMS is overpriced" anymore, especially when compared with data.

[Pxtl]

Wifi is free and Hangouts messages are tiny anyways. The bigger concern is avoiding accidentally sendning a message to a user who isn't connected to Hangouts through their primary device - I've often found Hangouts messages waiting for me on my tablet at home.

[dragonwriter]

> Wifi is free

In places that have free WiFi (or where you've already paid for it), WiFi is free or at least has a zero marginal cost per byte. But that's usually not everywhere people use phones.