[eru]

Why would the phone manufacturer care?

(And in any case, as you suggest most people pay more per bit transmitted on a mobile voice call than they pay per bit as data.)

Purely for fun, it would be interesting to hack up two smart phones to transmit data over a voice call. Presumably, you can keep everything binary, if you control the end-points.

[kevin_thibedeau]

That's how SMS works. It's running a baseband modem over the voice channel.

[lxgr]

SMS is transmitted over digital signaling or transport channels. There was never any analog coding involved (except for a few retrofitted implementations on landlines in Europe).