is there a place for a middle man?

Could Google, Apple or some other company negotiate a cheaper per minute call agreement with all/any of the other carriers? That way, no matter what device I had (device independent would be a key feature here), I would have an APP with an account with this new service (no contract?), which would then place the call out via their connections - for the cheapest rate for the dialed #.

See my previous blog post - which lead me into this thought.