Vodafone has defended its new charging structure for making mobile calls overseas, following a complaint from a consumer who saw the per-minute cost of his roaming calls jump by over 900 per cent.

Vodafone launched its new roaming service, Vodafone World, in May with the promise that it would bring reductions of 10-40 per cent for roaming in key holiday destinations.

However, the price of making calls back home from and within an overseas country and receiving calls from Ireland has increased dramatically in some cases.

Mr Alex Chirtoaca, who regularly travels to Moldova, used to pay 24-40c per minute for making calls within the country. These calls now cost €2.19 per minute under Vodafone World.

Prior to its introduction, calls in Moldova using a Vodafone phone cost 24c per minute for calls within the Voxtel network and 40c per minute for calls to local landlines or rival mobile networks in Moldova. Mr Chirtoaca confirmed these rates with a Vodafone customer service representative before travelling to the country in April.

But on May 17th, Moldova became part of the most expensive zone for roaming: Far Europe or Zone 5. The zone now has a flat rate of €2.19 per minute for making calls both within Moldova and back home to Ireland.

Mr Chirtoaca did not check the roaming rates before his next trip, which took place just one month later near the end of May. He was then shocked to receive a bill showing that he was charged €1.80 for making calls that lasted as little as nine seconds.

Mr Chirtoaca made several of these calls in the expectation that they would incur a charge of about 19-33c, as similar calls had done on his previous bill.

Mr Chirtoaca is particularly concerned that he was not notified of the new rates on his bill or through a text message from the operator, despite regularly receiving text messages advertising special discounts on picture messages.

He has since noted that rival operator O2 charges 39c per minute for all calls to local networks in Moldova. Calls to Ireland cost €1.18-€1.31.

However, he is reluctant to switch operators because he frequently avails of Vodafone's "call a friend for free" option.

He now intends to buy a new SIM card when in Moldova. These cards cost €10 but local calls can then be made at 12c per minute, he says.

A spokeswoman for Vodafone said 90 per cent of all its roaming calls were in Zone 1 (UK & Channel Islands) or Zone 2 (Near Europe) and that only one in every 4,000 occurred in Moldova.

"The vast, vast majority of all Vodafone customers can look forward to cheaper roaming, but there are going to be anomalies within that," she said. "In order to go from 4,000 separate rates to flat rates for five zones, there were going to be a few random areas where prices increased."

Other countries where roaming tariffs increased include Australia, where the charge-per-minute for post-paid Vodafone customers receiving calls from Ireland went up from €1.31 (off-peak) or €1.77 (peak) on Vodafone's Australian network to €1.99 at all times. The cost of making calls to Ireland also rose.

The regulating body for mobile operators, the Commission for Communications Regulation (ComReg), is currently in the middle of a consultation period for a code on tariff transparency.

The regulator believes customers should be notified of any changes or adjustments in tariffs before they occur. However, it is expected that the format of how this is done will be left to the individual operators.

The new code, due to be published at the end of July, will say that tariffs should be accurate and up-to-date, comprehensive and accessible.

Vodafone said it promoted its new service to customers in a full media campaign around the time of its launch, including advertisements in daily national newspapers, consumer and business magazines and airports. It also updated its website and sent direct mail to 150,000 high-frequency roamers.

ComReg's consumer guide to controlling the cost of using Irish mobile phones abroad is available at www.comreg.ie