(BRUSSELS) - The European Commission warned Thursday it had mobile telephone operators that overcharge users in its sights after finding some companies were rounding up call durations to bill customers more.

"There is an interesting and worrying phenomenon that the commission and national regulators have identified," commission spokesman Martin Selmayr told reporters.

"In some cases, operators are charging you for a call of one minute, two seconds what they can charge you for two minutes. This is a result of not charging by the second."

Selmayr said the commission may address the problem when EU Telecommunications Commissioner Viviane Reding presents plans in late September or early October to tackle the cost of mobile phone calls made while abroad in the bloc.

France, Lithuania, Portugal and Spain already have legislation in place that requires operators to charge by the second.

The practice of rounding up call durations by the minute undermines the effectiveness of EU caps on the price of making and receiving calls while abroad, which is known as roaming.

The caps, which mobile operators fought bitterly against, took effect a year ago and are set to be lowered over the weekend across the 27-nation European Union.

Telecoms specialist Levi Nietvelt at the BEUC European consumers association said that when the EU cap on voice calls was introduced, "a lot of operators resorted to billing whole minutes and not the exact amount (of time) the consumer uses."

However, operators dispute such claims.

"Most operators did not change their billing system since the introduction of the roaming regulations," said David Pringle, spokesman for industry body GSM Association.

He said that all ways of billing were acceptable "as long as operators are transparent."

Pringle said rules imposing billing by the second could even hurt competition because billing is "a difference that operators can use to attract consumers with different preferences."

The European Commission has also put pressure on operators over the cost of sending cross-border text messages and using mobile Internet services while abroad, which it considers to be too high.

It said in July that it aimed to bring forward a proposal to regulate prices of text message roaming, which could take effect by the summer travel season of 2009 and could halve the price of sending text messages while abroad in the EU.

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