A host of new mobile phone operators are likely to enter the Irish marketplace following a decision by telecoms regulator, Ms Etain Doyle, to support companies who wish to access the mobile phone networks of Eircell and Esat Digifone.

However, resellers of airtime - as practised by Cellular 3 which offers the Imagine mobile phone service - will not be supported by the regulator.

The regulator's decision should facilitate the entry of mobile virtual network operators (MVNO's) into the Irish marketplace which would increase competition and reduce prices for consumers.

Such operators offer mobile phone services by using the networks of existing mobile companies. Virgin Mobile, Mr Richard Branson's MVNO, has become popular in the UK market with more than 400,000 customers.

Companies which expressed an interest in getting involved in the mobile market in the Republic during the consultation period for the decision included the multinationals MCI Worldcom and NTL.

Up until now it has been left to individual telecoms companies to enter commercial negotiations with the two dominant mobile operators to gain access to their networks.

This enabled the two dominant networks to maintain high interconnection rates and prevent effective competition.

But in the ruling yesterday, Ms Doyle said she would intervene on a "case by case" basis and consider action to facilitate competition and to maximise the benefit to users.

She said that Eircell and Esat Digifone would both have to negotiate interconnection rates and Eircell would have to apply cost orientated rates to interconnection.

A failure to follow the regulator's decision would result in the operators being in breach of their licence.

Ms Doyle said she was also considering tying the competition to award third generation mobile phone licences to an operator's willingness to allow other companies to gain access to its networks and the pricing charged to these companies.

But Ms Doyle said regulatory intervention would not be warranted for resellers of airtimes. The benefits to consumers from simple resale were limited in nature, she said.

Mr Brian O'Donohoe, chief executive of the mobile phone operator Imagine, which resells airtime to customers, said he was disappointed by the decision.