A prisoner has taken legal action to try to stop inmates being charged "inflated" prices for phone calls.
BT charges inmates more than public call box users, it is claimed
Richard Davison, an inmate at HMP Elmley, Kent, claims the prices - more than five times the national call box rate - are a breach of human rights.
BT runs the phone system and charges are set with the Prison Service.
BT said the prison system costs more to run than public payphones while the Prison Service said it felt costs were fair to both inmates and the taxpayer.
Davison's solicitors, Leigh Day and Co, have applied for a judicial review of the practice in the High Court.
They claim prisoners currently pay 10p for the first 55 seconds of a call, then 1p per every 5.5 seconds after for local or national calls to landlines.
The cost of calls from BT public payphones is 40p for the first 20 minutes followed by 10p for each subsequent 10 minutes, they say.
Davison, who is serving 12 years for drug offences and has been an inmate since 2003, first raised the issue of unfair phone charges two years ago.
He complained to the prisons ombudsman Stephen Shaw, who investigated his complaint and published a report on the matter in 2006.
The complaint was upheld and Mr Shaw recommended the Prison Service negotiate with BT to reduce the charges. The recommendation was rejected.
Davison's legal team claim the charges are exacerbated by the fact that prisoners earn on average £8 a week.
There is also no system enabling prisoners to accept incoming phone calls.
The judicial review application, made last week, was supported by prisoner charities which said the current charges are not conducive to maintaining good family relationships.
Lucy Gampell, Director of Action for Prisoners' Families said: "Phone calls are a lifeline for families of prisoners, but the exorbitant cost of calls means that prisoners are limited to brief conversations.
"If a prisoner has more than one child, the limited time means it can be very difficult to speak to each one.
"Innocent children and families are being penalised by these charges. Around a quarter of families only use mobile phones and these costs are even more expensive."
Francesca Cooney, advice and information manager at the Prison Reform Trust, said: "We have had calls from people who say they can't have reasonable time with their partners.
"We are concerned that the high costs make it more difficult for people to maintain contact with their families."
Home Secretary John Reid, who has overall responsibility for the Prisons Service, is now expected to send his response to the judicial review application to the High Court.
A judge will then decide whether or not the judicial review should go ahead.
A BT spokesman said: "The public payphone service and the prison pin phone system are distinctly different services.
"The similarity is that both offer the ability for customers to make a telephone call.
"However, the public payphone service does not require the same level of ongoing investment in security and monitoring that are essential to meet the bespoke requirements of our customer Her Majesty's Prison Service.
"The two services are not comparable from an investment or operational perspective and this is reflected in each of the different approaches to pricing of the respective services."
A Prison Service spokesman said: "The Prison Service is satisfied that the current policy of telephone costs is fair both to prisoners and the taxpayer since any reduction in the cost of prisoner calls would require a subsidy."