"Telecoms regulator Ofcom says it is "very concerned" about the rising cost of calling directory enquiries and plans to examine the situation.
One popular enquiry service - 118 118 - recently increased its prices to a minimum of £8.98.
But Ofcom says some firms charge even more than that - up to £10.50 a call.
In a previous enquiry the watchdog decided against imposing a stipulated price cap on such charges, but it could now review that decision.
Under the current system operators are therefore free to charge up to a maximum of £23.97 for calls of less than a minute.
Anyone calling 118 pays two separate charges:
A flat-rate connection fee, which Ofcom says is typically up to £7.
A per-minute charge of up to £3.50. However, Ofcom says some providers "may charge significantly more".
In addition, there is an access charge of up to 50p a minute from the telecoms operator.
"Ofcom is very concerned about the rising prices of some 118 numbers, and we are already planning to review this market to ensure prices are transparent and fair to consumers," an Ofcom spokesperson said.
It said it would announce further details soon.
'Shock bills'
Some 118 services are far cheaper: Verizon UK, for example, charges a flat rate of 35p a call.
Other phone services that carry advertising and automated responses are free.
Many internet services are also free to users.
However, Citizens Advice said the current system leaves elderly people particularly vulnerable to high call charges.
It said one client had called them after receiving a £150 bill for calling a 118 number.
"Often it is unclear just how expensive a call can be," said Gillian Guy, chief executive of Citizens Advice.
"Elderly people who aren't confident using the internet are most at risk of shock 118 bills because they use these services to find information instead."
Ofcom said it was also aware of one consumer who called directory enquiries in 2009, and ended up with a bill for £350.
call centre operator"

http://www.bbc.co.uk/news/business-39842723

Ofcom have been given a substantial nudge... http://www.fairtelecoms.org.uk/docs.html?dqbr1
http://www.fairtelecoms.org.uk/uploads/1/1/4/5/11456053/dq_br.pdf

Revelations of specific cases and additional details  are now adding flesh to the story.