Mobilni operater će aktivirati SIM karticu.

• Mobilni operater = the subject of the sentence
• će = the future-tense auxiliary in 3rd person singular
• aktivirati = the main verb in the infinitive
• SIM karticu = the direct object

So the structure is basically:

subject + future auxiliary + main verb + object

Serbian often forms the future with a form of hteti (to want / will) plus the infinitive.

Here:

• će = will for he/she/it
• aktivirati = to activate

So će aktivirati literally works like will activate.

Other examples:

• Ja ću uraditi = I will do
• Oni će doći = They will come

Because će is a clitic in Serbian. Clitics usually go in the second position of the sentence or clause.

So in:

Mobilni operater će aktivirati SIM karticu.

the first unit is Mobilni operater, and će comes right after it.

This is very normal in Serbian. English speakers often expect the future marker to sit directly before the main verb, but Serbian word order works differently here.

Because karticu is in the accusative singular, since it is the direct object of the verb.

The base form is:

• kartica = card nominative singular

But as a direct object, it becomes:

• karticu = accusative singular

This is a very common pattern for feminine nouns ending in -a:

• knjiga → knjigu
• poruka → poruku
• kartica → karticu

Because adjectives in Serbian must agree with the noun they describe in gender, number, and case.

Here, operater is:

• masculine
• singular
• nominative

So the adjective also appears in the matching form:

• mobilni operater

This agreement is something English does not do, so it often stands out to learners.

In this sentence:

• mobilni operater is in the nominative because it is the subject
• SIM karticu is in the accusative because it is the direct object

So the sentence shows a very common Serbian pattern:

• subject in nominative
• object in accusative

Usually no. SIM is an abbreviation, and in this phrase it stays unchanged.

The case ending appears on kartica / karticu, not on SIM:

• SIM kartica = nominative
• SIM karticu = accusative

So SIM stays the same, while kartica changes.

Serbian does not have articles like English a and the.

So:

• mobilni operater can mean a mobile operator or the mobile operator
• SIM karticu can mean a SIM card or the SIM card

The exact meaning depends on context, not on an article.

This is one of the biggest differences from English.

No, Serbian word order is fairly flexible.

The sentence as given is the most neutral, straightforward order:

Mobilni operater će aktivirati SIM karticu.

But Serbian can move parts around for emphasis, for example:

• SIM karticu će aktivirati mobilni operater.

That might put more focus on SIM karticu or on mobilni operater, depending on context.

However, the clitic će still tends to stay near the second position, so that part follows a special rule.

A rough guide:

• će sounds approximately like a very soft che or tye
• karticu is roughly KAR-ti-tsu

Important details:

• ć is a soft Serbian sound that English does not have exactly
• c in Serbian is always like ts, never like English k or s

So:

• će ≈ soft che
• karticu ≈ KAR-ti-tsu

Yes. Serbian often leaves out the subject when it is clear from context.

So if the context already makes it obvious who is being talked about, you might hear:

Aktiviraće SIM karticu.

That still means will activate the SIM card.

The full version with Mobilni operater is more explicit because it names who will do the action.

Yes. Serbian commonly uses both Latin and Cyrillic scripts.

In Cyrillic, this sentence is:

Мобилни оператер ће активирати СИМ картицу.

So the grammar stays the same; only the script changes.