Večeras ću pozvati sestru telefonom.

Ću is the 1st person singular auxiliary used to form the future tense in Serbian.

In Večeras ću pozvati sestru telefonom, the pattern is:

• ću = I will
• pozvati = infinitive of the main verb, to call

So ću pozvati means I will call.

This is the usual way to form the future in standard Serbian:

• ja ću doći = I will come
• ti ćeš videti = you will see
• oni će otići = they will leave

This is about verb aspect, which is very important in Serbian.

• zvati is imperfective
• pozvati is perfective

In this sentence, pozvati is used because the speaker is talking about one completed action in the future: making a call once, successfully, as a whole event.

A rough comparison:

• zvaću sestru can suggest I’ll be calling my sister / I’ll call my sister in a more ongoing or repeated sense, depending on context.
• pozvaću sestru / ću pozvati sestru suggests I’ll give my sister a call as a single completed act.

English often does not force this distinction, but Serbian usually does.

Because sestru is the accusative singular form of sestra.

The verb pozvati takes a direct object: you call someone. Direct objects in Serbian usually go into the accusative case.

So:

• sestra = sister (dictionary / nominative form)
• sestru = sister (as the direct object)

Compare:

• Sestra dolazi. = My sister is coming.
  (sestra = subject, nominative)
• Pozvaću sestru. = I will call my sister.
  (sestru = object, accusative)

Telefonom is the instrumental singular of telefon.

The instrumental case is often used to express the means or instrument by which something is done. Here it means by phone / using the phone.

So:

• telefon = phone
• telefonom = by phone / with the phone

This is similar to:

• autobusom = by bus
• kolima = by car
• nožem = with a knife

In this sentence, telefonom tells you how the speaker will call.

Usually yes, in this kind of sentence it means by phone, over the phone, or simply on the phone.

So pozvati sestru telefonom is naturally understood as to call one’s sister by phone.

Serbian often uses the instrumental here where English uses a preposition:

• telefonom = by phone
• mejlom = by email

Because Serbian often omits subject pronouns when the verb already makes the subject clear.

Here, ću already shows 1st person singular, so I is understood.

So:

• Večeras ću pozvati sestru telefonom. = Tonight I will call my sister on the phone.

You could say:

• Ja ću pozvati sestru telefonom.

But ja is usually added only for emphasis, contrast, or clarity:

• Ja ću pozvati sestru, a ti pozovi brata.
  = I’ll call my sister, and you call your brother.

Because ću is a clitic, and clitics in Serbian usually appear in second position in the sentence or clause.

That is why Serbian often places ću after the first word or phrase:

• Večeras ću pozvati sestru telefonom.
• Sutra ću raditi.
• Ja ću doći.

This can feel unusual to English speakers, because English keeps will directly before the main verb. Serbian does not always do that.

You can also say:

• Pozvaću sestru večeras.

That is another normal future form, where the auxiliary is attached to the verb.

Yes. Serbian word order is fairly flexible, because case endings show grammatical roles. But changing the word order can change emphasis.

For example:

• Večeras ću pozvati sestru telefonom.
  Neutral; focus often starts with tonight.

• Sestru ću pozvati večeras.
  Emphasis on my sister.

• Telefonom ću pozvati sestru večeras.
  Emphasis on by phone.

• Pozvaću sestru večeras.
  Very natural, slightly more compact.

Not every possible order sounds equally natural in every context, but many are grammatically correct.

Večeras means this evening / tonight.

It refers specifically to the evening of today, not just any evening.

Compare:

• večeras = tonight / this evening
• svako veče = every evening
• uveče = in the evening
• jedne večeri = one evening

So Večeras ću pozvati sestru telefonom means the action will happen this evening, not tomorrow or at some unspecified future time.

Yes. It is pronounced approximately POZ-va-ti, with the zv cluster kept.

A rough guide:

• večeras ≈ VE-che-ras
• ću ≈ something like chyu, though English has no exact match
• pozvati ≈ POZ-va-ti
• sestru ≈ SES-tru
• telefonom ≈ te-le-FO-nom

A few important notes:

• č is like ch in church, but harder.
• ć is softer than English ch.
• Stress is not usually marked in normal writing, so learners often need to hear it from audio or a speaker.

Yes, that is possible, but it is not exactly the same.

• Večeras ću pozvati sestru telefonom
  = I will call my sister tonight.
  This sounds like one complete act.

• Večeras ću zvati sestru telefonom
  = I’ll be calling my sister tonight / I’ll call my sister tonight.
  This can sound a bit more ongoing, less bounded, or sometimes more neutral depending on context.

In many everyday situations, both could be used, but Serbian speakers often choose one or the other based on aspect and how they view the action.

Because Serbian often expresses this idea with the instrumental case alone, without a preposition.

English says:

• by phone
• with a phone
• on the phone

Serbian can simply say:

• telefonom

This is a normal feature of case-based languages: the ending itself helps express the relationship, so a preposition is not always needed.