Volunteers beginning of Bungalow Bill (3)
I believe the answer is:
tab
'bill' is the definition.
(tab is a kind of bill)
'volunteers beginning of bungalow' is the wordplay.
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'beginning of' says to take the initial letters.
The initial letter of 'bungalow' is 'b'.
'ta'+'b'='TAB'
(Other definitions for tab that I've seen before include "Marker" , "Till bill" , "Flap; meal bill" , "Running bar bill" , "Text indent key" .)