General conditions may impose such requirements as OFCOM consider appropriate for securing that every end-user of a public electronic communications service is able, by means of that service—
to make calls or otherwise transmit electronic communications to every normal telephone number; and
to receive every call or other electronic communication that is made or transmitted to him using such a service from apparatus identified by a normal telephone number.
A normal telephone number is one which—
has been made available, in accordance with the National Telephone Numbering Plan, as a number to be used for the purpose of identifying the destination for, or the recipient of, electronic communications; and
is for the time being—
a number adopted by a communications provider to be used for such a purpose; or
a number in use for such a purpose by a person other than a communications provider to whom it has been allocated in accordance with conditions under section 59.
In this section "electronic communication" has the same meaning as in section 56.