It's a little bit complex now. The incumbent carrier (ILEC) is still required to lease lines at the Central Office, but they used to be required to lease access to DSL delivered from remote terminals as well. AT&T still provides leased access to DSL delivered from remote terminals, but does not provide leased access to U-Verse, so companies leasing access can put their own DSLAMs in the central office and compete on speeds for users near the central office, but not in areas that are primarily served by remote terminals after AT&T rolls out U-Verse's ADSL2 and VDSL based DSLAMs; the leased access for users behind remote terminals is limited to 6mbps ADSL1.
In cities which have been dense for a long time, like San Francisco, there are lots of central offices, and competition using leased access is feasible, but in cities where density is more recent, such as San Jose, there may only be one central office, and there's only a small area with feasible competition with leased access.
In cities which have been dense for a long time, like San Francisco, there are lots of central offices, and competition using leased access is feasible, but in cities where density is more recent, such as San Jose, there may only be one central office, and there's only a small area with feasible competition with leased access.