Local residents in Summerhill, near Amroth, have expressed concern regarding the quality of their phone line.
The concentrator on telephone lines in the area has been affecting the efficiency of the service for many years.
Plaid AM Nerys Evans has written to the chief executive of BT on behalf of local residents to raise the issue.
She said: "Having a concentrator on your telephone line means that you are ultimately sharing your line with other people in the area. This means you can't use your phone if a certain number of your neighbours are using their phones at the same time and, of course, makes it impossible to receive broadband.
"Recently I've received numerous complaints from residents in Summerhill who are concerned with the quality of service in the area.
"I've written a letter asking how can they justify charging the residents of Summerhill full line rental when they are sharing their telephone lines. I've also asked when they intend taking residents off line concentrators so that they can have the full service that they are paying for."