If memory serves, Jake Thakeray used to sing it as follows:

THE TELEPHONE SONG by Sydney Carter

Standing alone in the damp and the dark
Of a filthy old phone box in Finsbury Park
I dialled Freemantle and got Waterloo,
But instead of the missus, I'm talking to you.

CHORUS
So, Say who you are, love, and not 'Hello'
Give me your name and give me your number.
Say who you are, love, and not 'Hello'
If I press button 'A' all my pennies will go.

The missus is waiting in Lancaster Gate,
I promised to phone at a quarter to eight.
I've done everything that it says I should do
But instead of the missus I keep getting you.

There's many the girl that I've got to know
Through a fault on the line of the GPO,
I'd do it again but it wouldn't be right.
I promised to phone up the missus tonight