Jag jämför mobiloperatörerna.

It breaks down like this:

• Jag = I
• jämför = compare / am comparing
• mobiloperatörerna = the mobile operators / the mobile phone providers

So the sentence structure is:

• Jag = subject
• jämför = verb
• mobiloperatörerna = object

Swedish is using a very normal subject–verb–object order here.

Because Swedish does not usually make the same simple present vs present continuous distinction that English does.

So:

• Jag jämför mobiloperatörerna can mean
  
  • I compare the mobile operators
  • I am comparing the mobile operators

Which one sounds best depends on context.

This is very common in Swedish. For example:

• Jag läser = I read / I am reading
• Hon jobbar = She works / She is working

It is the present tense.

The infinitive is att jämföra = to compare.

A few useful forms are:

• att jämföra = to compare
• jämför = compare / compares / am comparing / is comparing
• jämförde = compared / was comparing
• har jämfört = have compared / has compared

One nice thing for English speakers: in Swedish, the present-tense verb form is the same for all persons:

• jag jämför = I compare
• du jämför = you compare
• han/hon jämför = he/she compares
• vi jämför = we compare

So Swedish verbs do not change the way English verbs do with I compare vs he compares.

Because Swedish usually puts the definite article at the end of the noun as a suffix.

Here:

• mobiloperatör = mobile operator
• mobiloperatörer = mobile operators
• mobiloperatörerna = the mobile operators

So the -na at the end is part of the definite plural form.

This is one of the biggest differences from English. Instead of saying the mobile operators, Swedish often says essentially mobile-operators-the.

Here are the main forms:

• en mobiloperatör = a mobile operator
• mobiloperatören = the mobile operator
• mobiloperatörer = mobile operators
• mobiloperatörerna = the mobile operators

So in your sentence, mobiloperatörerna is:

• plural
• definite
• the direct object of the verb

Because mobiloperatörerna is already definite.

In Swedish, you normally do not add en/ett in front of a noun that already has a definite ending.

So:

• en mobiloperatör = a mobile operator
• mobiloperatören = the mobile operator

Not:

• en mobiloperatören ❌

For the plural:

• mobiloperatörer = mobile operators
• mobiloperatörerna = the mobile operators

Not always.

In your sentence, Jag jämför mobiloperatörerna, the verb simply takes a direct object:

• I am comparing the mobile operators

This is fine on its own and usually implies that you are comparing them with each other.

If you want to say what something is being compared with, Swedish often uses med:

• Jag jämför mobiloperatörerna med varandra.
  = I compare the mobile operators with each other.

• Jag jämför Telia med Telenor.
  = I compare Telia with Telenor.

So the short sentence is completely natural, but Swedish can also add med when needed.

A rough guide is:

• jämför ≈ YEM-fur
  but with Swedish vowel sounds, not exact English ones

A few important points:

• j in Swedish is often like English y
• ä sounds somewhat like the vowel in air or bed, depending on accent
• ö is a rounded vowel that English does not really have

So jämför is not pronounced like an English j word.

Also, the stress is on the first syllable:

• JÄM-för

It means a mobile operator, that is, a company that provides mobile phone service.

Depending on context, English translations could be:

• mobile operator
• mobile provider
• cell phone carrier
• network operator

So mobiloperatörerna could refer to companies like major phone carriers.

No, this is the basic Swedish word order:

• Jag = subject
• jämför = verb
• mobiloperatörerna = object

So it follows normal SVO order, just like English:

• I compare the mobile operators

However, Swedish is a verb-second language, which means that if something else comes first, the verb still stays in second position:

• Nu jämför jag mobiloperatörerna.
  = Now I am comparing the mobile operators.

Notice that jag moves after the verb when Nu comes first.

Yes, but it changes the meaning.

• Jag jämför mobiloperatörerna = I am comparing the mobile operators
  (specific ones, known in the context)

• Jag jämför mobiloperatörer = I compare mobile operators
  (more general, not specifically the operators)

So the version with -erna is definite and specific, while the version without it is indefinite and more general.

There is no adjective in this sentence, so the normal definite suffix is enough:

• mobiloperatörerna = the mobile operators

If you added an adjective, Swedish would usually use both a separate definite marker and the definite noun form:

• de stora mobiloperatörerna = the big mobile operators

That is different from your original sentence, where there is no adjective, so only the ending is needed.

Yes, it is natural.

It sounds like something someone might say when talking about researching phone plans or providers, for example:

• Jag jämför mobiloperatörerna innan jag byter abonnemang.
  = I’m comparing the mobile operators before I switch subscription.

On its own, the sentence is short but completely normal.