Una vez que terminé, llamé.

Una vez que means once or once that / after in the sense of as soon as something has happened.

In this sentence, Una vez que terminé, llamé means Once I finished, I called.

It introduces a clause that sets up the first action:

• Una vez que terminé = once I finished

Then the main clause gives the next action:

• llamé = I called

It is a very common way to connect two actions in time.

They are in the preterite because both actions are seen as completed events in the past.

• terminé = I finished
• llamé = I called

The sentence describes a sequence:

1. I finished
2. I called

Since both happened and are over, Spanish uses the preterite.

Because this sentence talks about a real completed action in the past, not a future or hypothetical one.

• terminé = preterite indicative, I finished
• termine = present subjunctive, often used for future or uncertain situations

Compare:

• Una vez que terminé, llamé.
  = Once I finished, I called.

• Una vez que termine, llamaré.
  = Once I finish, I’ll call.

So in your sentence, terminé is correct because the finishing already happened.

Spanish often leaves out subject pronouns when the verb ending already makes the subject clear.

• terminé clearly means I finished
• llamé clearly means I called

So yo is unnecessary here.

You could say:

• Una vez que yo terminé, llamé.

But that would usually add emphasis or contrast, for example if you want to stress I finished, not someone else.

Terminé is:

• the first-person singular form
• of terminar
• in the pretérito indefinido (preterite)

So:

• terminar = to finish
• terminé = I finished

This is the regular -ar preterite ending for yo:

• -é

Example pattern:

• hablar → hablé
• llamar → llamé
• terminar → terminé

Llamé is:

• the first-person singular form
• of llamar
• in the preterite

So:

• llamar = to call
• llamé = I called

It follows the same regular -ar preterite pattern:

• llamar → llamé

The accent marks show where the stress goes and also help distinguish these forms from other verb forms.

• terminé is stressed on the last syllable: ter-mi-NÉ
• llamé is stressed on the last syllable: lla-MÉ

These accents are a normal part of the yo preterite forms of regular -ar verbs.

They also help distinguish them from forms without an accent:

• termine = subjunctive / formal command context
• llame = subjunctive / formal command context

So the accent is important both for pronunciation and grammar.

The comma separates the introductory time clause from the main clause.

• Una vez que terminé, = introductory clause
• llamé. = main clause

This is very natural in Spanish, especially when the sentence begins with a clause like cuando, después de que, una vez que, etc.

You may sometimes see short sentences without a comma in informal writing, but the comma here is standard and clear.

Yes. You can also say:

• Llamé una vez que terminé.

This means the same thing: I called once I finished.

The version with Una vez que terminé, llamé puts more focus on the time sequence and sounds very natural.

So both are possible:

• Una vez que terminé, llamé.
• Llamé una vez que terminé.

The difference is mainly one of emphasis and style, not basic meaning.

Yes, often you can.

• Una vez que terminé, llamé.
• Una vez que acabé, llamé.

Both can mean Once I finished, I called.

In many contexts, terminar and acabar are close in meaning. However, terminar often feels a bit more neutral and straightforward for to finish.

Spanish speakers may choose one or the other depending on habit, region, or what exactly is being finished, but both are common and natural.

They are similar, but not always exactly the same.

• Una vez que terminé, llamé.
  = Once I finished, I called.

• Cuando terminé, llamé.
  = When I finished, I called.

In many past contexts, they are very close. But una vez que more strongly emphasizes that the second action happened after the first one was completed.

So:

• cuando = when
• una vez que = once / once it had happened

Yes. In Spanish, llamar often means to call in the sense of to phone someone.

So llamé can naturally mean:

• I called
• I phoned

In everyday Spanish from Spain, that is a very normal use of llamar.

It works perfectly well in Spain and also in most other Spanish-speaking countries.

Nothing in Una vez que terminé, llamé is especially regional. It is standard, widely understood Spanish.

The main thing that may vary by region is which past tense speakers prefer in some situations, but this sentence itself is completely normal and correct across the Spanish-speaking world.