Prijenos broja počinje sutra.

Because broja is the genitive singular form of broj.

The noun prijenos often takes a noun in the genitive, so prijenos broja literally means transfer of a number or, in context, number transfer / number porting.

• broj = number
• broja = of a number

So this is a very normal Croatian structure.

Prijenos means transfer, moving, or transmission, depending on context.

In this sentence, it most naturally means transfer/porting of a phone number. In telecom language, prijenos broja is the standard way to say number porting.

It comes from the verb family related to prenijeti / prenositi, meaning to transfer or to carry over.

Počinje is the 3rd person singular present tense form of počinjati.

Here it means:

• it starts
• it is starting

The subject is prijenos broja, which is grammatically singular, so the verb is singular too:

• prijenos = singular
• počinje = singular verb form

Because Croatian, like English, can use the present tense for scheduled or expected future events.

So Prijenos broja počinje sutra is similar to English:

• The transfer starts tomorrow

This sounds natural when talking about a planned event, timetable, or arranged process.

A more explicit future is also possible, for example:

• Prijenos broja počet će sutra.

But počinje sutra is very natural in everyday usage.

Sutra means tomorrow.

In this sentence, it comes at the end:

• Prijenos broja počinje sutra.

That is a very normal placement. Croatian word order is flexible, though, so you could also say:

• Sutra počinje prijenos broja.

This puts more emphasis on tomorrow.

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

The most neutral version here is:

• Prijenos broja počinje sutra.

But you may also hear:

• Sutra počinje prijenos broja.

Both mean the same thing, but the emphasis changes a little:

• starting with Sutra highlights when
• starting with Prijenos broja highlights what

So the original sentence is neutral and natural.

Because Croatian does not have articles like English a and the.

So Croatian simply says:

• Prijenos broja počinje sutra.

English has to choose something like:

• The number transfer starts tomorrow
• Number porting starts tomorrow

Which one sounds best depends on context, but Croatian does not mark that difference with an article.

Literally, broj just means number.

But in this context, prijenos broja usually refers to a phone number. This is especially common in mobile or telecom situations, where it means transferring your number to another provider.

So the full idea is usually understood as:

• phone number transfer
• number porting

Yes.

You could say:

• Prijenos broja počet će sutra.

That is a straightforward future form: will start tomorrow.

Compare:

• počinje sutra = starts tomorrow, often used for scheduled events
• počet će sutra = will start tomorrow, more explicitly future

Both are correct. The original sentence sounds very natural and slightly more matter-of-fact or scheduled.

A simple approximate pronunciation is:

Pree-yeh-nos BRO-ya PO-chee-nyeh SOO-tra

A few helpful notes:

• prij in prijenos sounds roughly like pree-ye
• j in Croatian is like English y
• č in počinje sounds like ch in chocolate
• nj sounds like the ny in canyon
• u in sutra is like oo in food

So počinje is roughly PO-chee-nyeh.