Mentioning Italian capital, use phone when abroad (4)
I believe the answer is:
roam
'use phone when abroad' is the definition.
(to use a different phone network when abroad)
'mentioning italian capital' is the wordplay.
'mentioning' shows a homophone (sound like).
'italian capital' becomes 'Rome' (capital of Italy).
'rome' is a homophone of 'ROAM'.
(Other definitions for roam that I've seen before include "Travel aimlessly" , "Ramble without purpose" , "Wander widely" , "Prowl" , "Rove or ramble" .)