You could be forgiven for thinking that owning a licence to run a mobile communications network in the Republic was an excuse to print money.

Eircell and Esat Digifone have already signed up half the population despite charging call rates that most experts believe are well above the EU average. And with no third generation licence (3G) auction to negotiate, both operators seem well set to reap the rewards of the mobile multimedia revolution.

But the good times may not last forever. In Geneva last month telecoms experts gathered to discuss a phenomenon that many believe could threaten the dominance of licensed mobile network operators. These new entrants to the telecoms arena are so called Mobile Virtual Network Operators and several will soon offer services in the Republic.

A virtual operator is an organisation that offers mobile subscription and call services to customers but does not have an allocation of spectrum. Instead it pays existing network operators for the use of their mobile networks.

A form of virtual operator already exists in the Republic. The Imagine mobile service and Spirit Mobile already offer voice services to more than 20,000 customers in the Republic. Both aspire to become full mobile virtual network operators and offer a full range of data services in the future.

They entered the market by buying mobile airtime in bulk from Eircell and selling it on at reduced rates. But the commercial agreement on which their services rest is the subject of legal action by Eircell, which is currently seeking to cancel the agreement in the High Court.

Other operators keen to enter the virtual mobile space have had little joy from negotiations with the incumbent mobile operators. "Negotiations are slow at present and I suspect a certain amount of natural resistance," says Mr Richard Brennan, director at Budget Telecom.

Budget Telecom has been negotiating for access to the mobile networks of Eircell and Digifone for months to enable it to provide its customers with indirect access to mobile networks by using a number prefix. It claims to be the victim of unnecessary delaying tactics.

An Eircell spokeswoman said the company rejected the idea that there were any delaying tactics. "This is a new and complex area and we believe that any agreement should be watertight. This is uncharted territory," she added.

In submissions to the telecoms regulator, both network operators have argued strongly that any arrangements should be commercially negotiated and in the interests of both the network operators and the virtual operator.

However, a recent decision by telecoms regulator, Ms Etain Doyle, could hold the key to wrenching open the networks of incumbent mobile operators. Ms Doyle has decreed that companies seeking to offer indirect access to mobile networks or full mobile virtual network operator services will now be backed up by regulatory power in their negotiations.

In a separate decision, which has enraged the two network operators, she has linked enabling access to mobile networks to the process to award third generation mobile licences. In other words, if Eircell and Digifone don't promise to enable access for competitors they could endanger their chances of obtaining a third generation licence.

So who is likely to take advantage of access to mobile networks in the Republic? The obvious contenders are the fixed line telecoms operators who understand the technology and are able to route calls from the mobile networks onto their own telecoms infrastructure to reduce call costs.

NTL, which is currently rolling out a £300 million (€381 million) digital network in Dublin, Waterford and Galway, is aiming to gain a foothold in the mobile market. A submission to the telecoms regulator from NTL, seen by The Irish Times, shows the company plans to deploy many of its interactive digital TV services, such as e-commerce banking and entertainment services, across mobile networks.

The company is considering bidding for a third generation mobile licence but there is speculation within the industry that it may seek to strike a deal with the third mobile operator Meteor to offer some form of a virtual mobile sevice.

Powerful new entrants from abroad are also seeking to enter the market as a means of establishing seamless pan-European mobile networks. Orange took part in the regulator's recent consultation process as did the pan-European operator Tele2.

Mr Peter Scrope, a director with Tele2, said the company had been in discussions with the licensed network operators and had already been allocated a mobile network code from the regulator. He said the company expected to launch a fixed and mobile service shortly.

But telecoms companies are not the only players hoping to get a slice of one of the world's fastest growing market. Richard Branson's Virgin Mobile has claimed 400,000 customers in the UK since April by leveraging the power of the Virgin brand and integrating services and content from the group's subsidiary operations.

The company is a 50-50 joint venture agreement with Deutsche Telecom's mobile network operator One-to-One. It has virtual mobile operations in Singapore and Australia, and is currently negotiating for entry into 30 markets, according to a spokesman for Virgin Mobile in the UK.

However, the possibilities are endless and go far beyond traditional telecoms companies.

A recent report by the technology consultancy Ovum suggested big consumer brands, such as Coca-Cola or Manchester United Football Club, could end up running mobile virtual network operators. But its not all bad news for incumbent operators. Mobile virtual networks promote easier international expansion. Eircom is actively seeking to establish a virtual mobile operation in the UK despite its subsidiary's reluctance to accept the concept in its home market.

Mr Hans Waagener, managing director of Eircom International, said the company had set a priority in achieving a virtual network agreement in the UK first and possibly into Europe later.

He said possible announcements on these type of agreements were more likely to happen closer to the launch of third generation networks in the UK.

And with increasing numbers of virtual operators setting up over the next few months, licensed operators will benefit from the fees they will charge virtual operators for access to their mobile networks.

Meanwhile, it is expected that the massive advertising campaigns by new entrants will boost the whole sector.