How much does it cost to call a cell phone in the US?
Twilio: $0.02/min to all US and $0.03 to UK landlines or $0.32 to UK mobiles -- yes, 16x the US rate.
Voxeo: $0.02/min to all US and UK landlines or between $0.14 and $0.35 for mobiles.
Google wouldn't use Twilio or Voxeo for this kind of service so it gets cheaper elsewhere -- especially on their scale -- but it shows the relative difference.
When I moved to France, unlimited and unrestricted calling plans didn't exist yet and the talking time was pretty measly. Even now their nights and weekend billings were awkward 8PM-Midnight, Saturday afternoons - Sunday Midnight. They gave you a feature that was practically worthless.
This explains why SMS took so long to get off the ground there. A message cost $0.15, which is about the cost of a voice call, and unlimited messaging plans were $15-20 in addition to your voice plan. That money could be better spent on an even bigger plan with 1000 minutes. That and T9 sucked as a keyboard interface.
Eventually, I hope the rest of the world gets real