The European Commission (EC) is to urge national telecomms regulators to take action over 15 cases of possible overcharging by mobile operators.
The cases involve calls received from other mobile networks or from fixed phones, Commission sources said.
The EC will send letters this week following its own inquiry, launched in January, which involved questionnaires to 50 mobile and fixed operators.
"In 15 cases there might be a pricing issue which we have to inquire in more detail. We are writing to national authorities saying that as a result of preliminary inquiries they should look at prices of their national operators," a commission source said.
The national regulators have until September to indicate whether they will take up the cases; if they do not the Commission will continue its own inquiries, he said.
Where national regulators do take action, the Commission will decide whether sufficient action has been taken in six months time, he said.
The Commission will not reveal which operators or countries are involved before it knows which national regulators are taking up the cases.
The Commission hoped the January launch of this inquiry would have its own impact in forcing down these charges but only Spain has lowered mobile to fixed rates.
Analysts believe mobile interconnection rates are the lowest in the Nordic region and higher in the rest of the European Union.
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