Mobilni operater ima roming i dopunu.

Because dopuna is the direct object of ima.

After imati in a sentence like this, the thing someone has is normally in the accusative case. For many feminine nouns that end in -a, the accusative singular ends in -u.

So:

• dopuna = nominative singular
• dopunu = accusative singular

That is why the sentence has ima dopunu.

Roming is also a direct object, so it is also in the accusative. But masculine inanimate nouns often have the same form in the nominative and accusative singular.

So:

• roming = nominative singular
• roming = accusative singular

That is normal in Serbian.
Compare:

• telefon → imam telefon
• internet → imam internet

So both objects are in the same case, but they look different because they belong to different noun patterns.

Ima is the 3rd person singular present tense of imati, which means to have.

Basic present-tense forms:

• imam = I have
• imaš = you have
• ima = he/she/it has
• imamo = we have
• imate = you have
• imaju = they have

Since mobilni operater is singular, the verb must also be singular: ima.

In this kind of context, it often means something like has available, offers, or provides.

So Mobilni operater ima roming i dopunu can mean that the operator has those services in its offer, not necessarily possession in the physical sense.

This is very common in Serbian. For example, a shop can imati something, meaning it carries or sells it.

Because adjectives in Serbian must agree with the noun they describe in:

• gender
• number
• case

Here, operater is:

• masculine
• singular
• nominative

So the adjective must also be masculine singular nominative: mobilni.

Compare:

• mobilni operater = masculine
• mobilna mreža = feminine
• mobilno plaćanje = neuter

Serbian normally does not use articles.

So mobilni operater can mean:

• a mobile operator
• the mobile operator

The exact meaning depends on context.

This is something English speakers often notice right away: Serbian leaves definiteness unstated unless the context makes it clear.

Yes. Serbian word order is more flexible than English word order.

The sentence as given:

• Mobilni operater ima roming i dopunu.

is a neutral, natural order: subject + verb + object.

You could also say:

• Mobilni operater ima dopunu i roming.

That only changes the order of the two objects, not the basic meaning.

A more unusual order is also possible for emphasis, but the given version is the most straightforward one for a learner.

Yes. It is a borrowed word, adapted to Serbian spelling.

English roaming becomes Serbian roming.

So this is one of many loanwords that may look familiar to an English speaker, but the spelling is adjusted to Serbian pronunciation and writing conventions.

In Cyrillic, it would be:

• роминг

In telecom context, dopuna usually means a top-up, recharge, or adding prepaid credit.

Depending on context, it can refer to:

• the action of topping up
• the top-up itself
• prepaid credit or a refill option

So in a sentence about a mobile operator, dopuna is best understood as top-up / recharge service.

You may also see related expressions such as:

• dopuna kredita = credit top-up
• dopuniti kredit = to top up credit