Most LLU operators only unbundle the broadband service leaving the traditional telephone service using BT's core equipment (with or without the provision of carrier preselect). Where the traditional telephone service is also unbundled (full LLU), operators usually prohibit the facility where selected calls can be made using the networks of other telephone providers (i.e. accessed using a three- to five-digit prefix beginning with '1'). These calls can usually still be made by using an 0800 or other non-geographic (NGN) access code.