Quando o celular voltar a funcionar, eu vou ligar para você.

Because Portuguese uses the future subjunctive after quando when the action is in the future.

So in Quando o celular voltar a funcionar..., voltar is not the infinitive here in terms of function; it is the future subjunctive form of voltar.

This is very common after words like:

• quando = when
• se = if
• assim que = as soon as
• logo que = once / as soon as

Examples:

• Quando eu chegar, te aviso.
• Se ele ligar, eu atendo.

English usually uses the present after when for future meaning, and Portuguese uses this special verb form.

Literally, it means to return to functioning.

In natural English, that usually becomes:

• to start working again
• to work again

So o celular voltar a funcionar means the phone is currently not working, and later it will work again.

A similar phrase is:

• voltar a chover = to start raining again
• voltar a estudar = to study again / go back to studying

Both are correct, but eu vou ligar is much more common in everyday Brazilian Portuguese.

Two ways to talk about the future:

• eu vou ligar = I’m going to call / I will call
• eu ligarei = I will call

In Brazil, the ir + infinitive future is usually more natural in speech.
The simple future (ligarei) can sound more formal, written, or less conversational.

So this sentence sounds very natural and modern.

It can mean both, depending on context.

Common meanings of ligar:

• ligar para alguém = to call someone
• ligar o celular / a TV / o computador = to turn on the phone / TV / computer

In your sentence, eu vou ligar para você, it clearly means I’m going to call you, because of para você.

Because the verb ligar, when it means to call someone, is commonly used with para in Brazilian Portuguese:

• ligar para alguém = to call someone

So:

• Vou ligar para você
• Ela ligou para mim
• Ele vai ligar para o escritório

In everyday Brazilian Portuguese, people also often say:

• vou te ligar

That means the same thing and is very common.

Yes. In Brazilian Portuguese, vou te ligar is very common and natural.

Compare:

• vou ligar para você = a bit fuller, very clear, completely natural
• vou te ligar = very common in conversation

Both are correct in Brazil.

A small note: você often goes with te in everyday Brazilian speech, even though some grammar books prefer more formal consistency. So native speakers very often say things like:

• Eu vou te ligar
• Eu te avisei
• Eu te vi

Because the sentence begins with a dependent time clause:

• Quando o celular voltar a funcionar

Then comes the main clause:

• eu vou ligar para você

In Portuguese, when this kind of introductory clause comes first, a comma is normally used.

So the structure is:

• When X happens, Y will happen.

You will see this pattern a lot:

• Quando eu chegar, a gente conversa.
• Se chover, eu fico em casa.
• Assim que ele responder, eu te conto.

Portuguese uses articles more often than English.

So o celular is very normal, even where English might simply say the phone or sometimes just my phone, depending on context.

Here, o celular probably refers to a specific phone already understood in the situation.

In Portuguese, articles are used a lot with nouns:

• o carro
• a casa
• o celular
• a internet

If the speaker wanted to be more specific, they could also say:

• meu celular = my cellphone

Yes, absolutely. That sounds natural too.

Compare:

• voltar a funcionar = to start working again
• funcionar de novo = to work again

They are very close in meaning.

A slight nuance:

• voltar a funcionar often highlights the idea of returning to a previous working state
• funcionar de novo is a bit more direct: work again

Both are good in everyday Brazilian Portuguese.

Yes, it could be tu, but você is much more widespread in Brazil.

So:

• eu vou ligar para você = very broadly natural in Brazil
• eu vou ligar para ti = used in regions where tu is common

Brazilian Portuguese varies by region. In some places, people use:

• você
• tu
• or both, depending on context

If you are learning general Brazilian Portuguese, você is a safe default.

Normally, no. That sounds unnatural here.

After quando referring to a future event, Portuguese usually does not use vai + infinitive in that clause. It uses the future subjunctive instead:

• Quando o celular voltar a funcionar...

This is one of the biggest differences from what English speakers may expect.

So the natural pattern is:

• Quando + future subjunctive, main clause

Examples:

• Quando ele chegar, sairemos.
• Quando você terminar, me chama.

Yes. Celular is the normal word in Brazil for cell phone / mobile phone.

In European Portuguese, the usual word is:

• telemóvel

So:

• Brazil: celular
• Portugal: telemóvel

If you are learning Brazilian Portuguese, celular is exactly the right word.

Yes. Portuguese often drops subject pronouns when the meaning is clear.

So these are both fine:

• Quando o celular voltar a funcionar, eu vou ligar para você.
• Quando o celular voltar a funcionar, vou ligar para você.

In Brazilian Portuguese, people often keep eu for emphasis, clarity, or rhythm, so its presence here is completely natural.

Yes. In everyday Brazilian speech, para is very often reduced to:

• pra
• sometimes pro / pra with articles

So in conversation, you will often hear:

• vou ligar pra você

This is extremely common and natural in spoken Brazilian Portuguese.

The full form para você is still correct and may appear more often in careful speech or writing.