Talk a lot and hang up (3)
I believe the answer is:
gas
'talk a lot' is the definition.
(gas can mean to talk at length)
'hang up' is the wordplay.
'hang' becomes 'sag' (I've seen this in another clue).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'sag' written backwards gives 'GAS'.
'and' is the link.
(Other definitions for gas that I've seen before include "Americans' petrol" , "Nitrogen maybe" , "Petrol (US)" , "could be embarrassing for American" , "Eg, oxygen" .)