Commonly known as LLU, this allows a third party service provider to supply the Broad Band element of a service over another parties telephone line.
In the diagram below you can see the Telephone and Broadband service provided to two homes.
The top part on the right hand side of the diagram below shows the ILEC supplying both telephony and broadband services.
The bottom part on the right hand side of the diagram shows a CLEC offering the Broadband element and the ILEC supplying the voice service.
It is now possible for the ILEC to offer both services. It is more likely they will offer IP telephony for this option.
Test access can help either party identify and diagnose faults quickly. As ownership of the circuit is split across several parties it is important to have a clear fault analaysis and repair startegy.