It's me, Marco.
Stress 'SON-o-io'. 'Io' = EE-oh.
Use this to identify yourself immediately when a close friend or family member answers. Since they know your number, it reinforces familiarity and speeds up the conversation.
'Sono io' = it's me (literally 'I am I'). In Italian, you never say 'sono' without a name or context when calling someone who may not recognise your voice. 'Sono io, [name]' is natural and warm. In formal contexts: 'Sono [Nome Cognome]' (I'm [First Last Name]).
Ciao, sono la mamma.
Hi, it's mum.
Family member identifying themselves.
Sono Luisa. Stai bene?
It's Luisa. Are you okay?
Name + immediate concern.
Indovina chi è!
Guess who it is!
Playful when calling a friend.
Italian family phone calls are characterised by warmth and extended greetings. Calling grandparents ('nonni') is a valued cultural practice, and many Italian families have regular Sunday phone calls. 'Chiama la nonna!' (Call grandma!) is a very Italian parental instruction.