Breakdown of Кто-нибудь звонил мне вчера?
звонить
to call
вчера
yesterday
мне
to me
кто-нибудь
anyone / someone (unspecified)
Questions & Answers about Кто-нибудь звонил мне вчера?
Why do we use кто-нибудь here instead of кто-то?
Both translate to someone or anyone, but they have a key difference. You use кто-нибудь when you are asking if anyone at all called, and the person's identity is completely unknown or hypothetical. You would use кто-то if you knew for a fact that a specific person called, but you just didn't know or forgot who it was.
Why is the verb звонил in the masculine singular form? What if the caller was a woman?
Why is the pronoun мне used here instead of меня?
Мне is the dative case of я (I). The Russian verb звонить (to call on the phone) always takes the dative case for the person receiving the call, because you are making a call to them.
Why use the imperfective verb звонил instead of the perfective позвонил?
When you ask a general question about whether an event simply happened or not in the past, without focusing on a specific result or completion, Russian strongly prefers the imperfective aspect. You are just asking about the fact of the action: did a call take place?