Phone users have been warned that they risk running up massive bills for using directory enquiries to get a telephone number.
Getting connected to a line through a directory enquiries service costs up to €30 for a 10-minute call, Consumers Association research has found.
The consumer lobby group found charges have shot up by 200pc in four years, with some operations charging up to €5.58 for a one-minute call.
Dermott Jewell of the Consumers' Association said it was a challenge to decipher the high charges imposed by the different directory enquiries services.
A comprehensive survey found that charges vary between 11811, 11890, 11888 and 11850, depending on which telecoms carrier is used to call the directory enquiry service.
A one-minute call to 11850 from an Eircom landline costs €5.58. If the call is made to 11850 from a pre-pay mobile with 3, the cost is €4.26.
The 11811 operation is part of Eircom.
Even a one-second call costs more than €5 to some directory enquiry providers.
This is because if you ring a directory enquiry number, you are automatically charged a connection fee the moment the call is answered.
Getting a phone number texted to a mobile costs €2.
But choosing to be connected to a line, after getting the number, can be hugely expensive.
Eircom customers are charged €30.69 for a 10-minute call transferred from 11850. With 02 the cost is €23.52 for a similar call made originally to 11811, 11890 or 11850.
However, before being transferred to the number that you want, an automated warning message is played outlining the charges.
The survey found that 11888 offers the lowest prices for those who use directory enquiries.
The Consumers' Association advised people who do not have a telephone directory to search for numbers online or on their smartphones.
Chief executive of Dublin-based 11890, Nicola Byrne, said the wholesale prices for using the services offered by her company were set by telecoms carriers such as Vodafone, O2, UPC and BT.
She also blamed the telecoms regulator ComReg. "It is nothing to do with us. I have been into ComReg complaining about it so often that they have banned me from the premises," she said.
A spokesman for Eircom's 11811 said the prices reflected a fall in consumer demand for directory enquiry services.
ComReg's spokesman said it did not set directory enquiry charges but had a role in ensuring they were transparent.