Push-me/Pull-you?

Interesting footnote to this week’s announcement of a network-sharing agreement between Telefonica (O2) and Vodafone.  According to the New York Times , the companies will continue to charge each other termination fees for calls between the two of them.  That is, they will continue to charge so-called ‘off-net’ fees for calls that actually remain within the jointly owned network.  Does this strike anyone else as slightly odd?  The NYT also reports that an investment fund manager - Sanford C. Bernstein & Company – has estimated that the network-sharing arrangement could generate savings of up to $1.9bn for each operator.  If the companies continue to raise off-net termination charges, will any of these savings be passed on to mobile customers?  Or is this a zero-sum-game?  Smarter thinkers please advise…