Some phone equipment that phone companies have installed on their lines can seriously degrade ADSL performance. For example, a T1 line installed for your neighbor can have a dramatic effect on your maximum DSL bandwidth. T1 lines and DSL use a lot of the same frequencies, this causes interference if used together in the same wire bundle. In addition, in some areas, load coils have been installed on the voice lines to improve the quality of voice service. Unfortunately, they do not allow any signals above the voice band 0-4kHz to pass through them.
Most telcos have a process in place to remove the load coil from the line.
However, it can add to the cost of your installation. This service provides 144K bps of bandwidth in both directions. However, there are no standards approved for this service. This service runs at approximately 6M bps. There are currently no standards set for this service.