what do we know about mobile termination comment on tommaso valletti and stephen littlechild jean tirole xièmes entretiens de l arcep economie des mobiles 26 mars 2007 1 i two way access operator 2 pays fee a c caller r net receiver s marginal cost t 9 off 1c o check different ways of fixing non cooperative determination ii negotiation iii under regulatory requirement reciprocal charges iv regulation 3