Prüfe die Rufnummernmitnahme, bevor du die SIM-Karte freischaltest.

Because Prüfe is an informal singular command: Check ...

German often forms a du-command by using the verb stem:

• prüfen → Prüf! or Prüfe!

So:

• Prüfe die Rufnummernmitnahme = Check the number transfer
• du prüfst die Rufnummernmitnahme = you check the number transfer / you are checking ...

In other words, Prüfe is not a normal present-tense statement; it is an instruction.

In German, the subject du is usually left out in informal commands.

So German says:

• Prüfe ... = Check ...

not usually:

• Du prüfe ... ❌

But after bevor, the clause is no longer a command. It becomes a normal subordinate clause, so it needs its subject:

• bevor du die SIM-Karte freischaltest = before you activate the SIM card

So:

• first part = command, no du
• second part = normal clause, so du is required

Because bevor introduces a subordinate clause, and in German subordinate clauses, the finite verb usually goes to the end.

Compare:

• Du schaltest die SIM-Karte frei. = You activate the SIM card.
• ..., bevor du die SIM-Karte freischaltest. = ..., before you activate the SIM card.

That final verb position is one of the most important word-order rules in German subordinate clauses.

Bevor means before.

It introduces an action that happens earlier than the action in the main clause:

• Prüfe die Rufnummernmitnahme, bevor du die SIM-Karte freischaltest.
• Check the number transfer before you activate the SIM card.

Because bevor is a subordinating conjunction, it sends the conjugated verb to the end of its clause.

Rufnummernmitnahme is a compound noun, which is very common in German.

It is made up of:

• Rufnummer = telephone number
• Mitnahme = taking along / transfer

Together, Rufnummernmitnahme means something like:

• phone number transfer
• number porting
• keeping your existing number when changing provider

German often combines several ideas into one noun instead of using a longer phrase.

Because Rufnummernmitnahme is a feminine noun.

The head of the compound is Mitnahme, and Mitnahme is feminine, so the whole compound is feminine:

• die Mitnahme
• therefore die Rufnummernmitnahme

In this sentence, die Rufnummernmitnahme is also the direct object of prüfen, so it is in the accusative case. For feminine nouns, the article stays die in both nominative and accusative:

• nominative: die Rufnummernmitnahme
• accusative: die Rufnummernmitnahme

Both are in the accusative case because both are direct objects.

1. Prüfe die Rufnummernmitnahme

   • You are checking what?
   • die Rufnummernmitnahme

2. ... bevor du die SIM-Karte freischaltest

   • You activate what?
   • die SIM-Karte

Since both nouns are feminine, the article is die in the accusative.

German often uses a hyphen when a noun includes:

• an abbreviation
• a letter sequence
• a foreign element
• something that would be hard to read as one word

So SIM-Karte is preferred over a solid form because SIM is an abbreviation.

This is very common in German:

• E-Mail
• USB-Stick
• Online-Shop
• SIM-Karte

The basic verb is freischalten = to activate / unlock / enable.

This is a separable verb:

• infinitive: freischalten
• normal main clause: du schaltest die SIM-Karte frei
• subordinate clause: ..., weil du die SIM-Karte freischaltest

So in a subordinate clause, the prefix frei- stays attached to the verb, giving:

• freischaltest

That is why you do not see frei separated here.

Yes. In many cases, both are possible in the informal singular imperative:

• Prüf die Rufnummernmitnahme.
• Prüfe die Rufnummernmitnahme.

Both are understood as Check the number transfer.

The version with -e can sound a bit more careful, standard, or written, while the shorter form is often common in everyday speech. In instructions and user interfaces, both can appear.

It would be:

• Prüfen Sie die Rufnummernmitnahme, bevor Sie die SIM-Karte freischalten.

Key changes:

• Prüfe → Prüfen Sie
• du → Sie
• freischaltest → freischalten

So the original sentence is clearly addressing one person informally, while this version is formal/polite.

Yes, prüfen works well here and means to check, to verify, or to examine.

Depending on context, German might also use:

• überprüfen = to verify / double-check
• kontrollieren = to check / inspect

But prüfen is very natural in instructions, technical steps, and service messages.

So:

• Prüfe die Rufnummernmitnahme sounds like Check whether the number transfer is in order / possible / correctly set up

Because in German, a subordinate clause introduced by bevor is separated from the main clause by a comma.

So:

• Prüfe die Rufnummernmitnahme, bevor du die SIM-Karte freischaltest.

This comma is required in standard German spelling.

A good rule: if you have a subordinating conjunction such as bevor, weil, dass, wenn, obwohl, you usually need a comma before the subordinate clause.

Yes. You could also say:

• Bevor du die SIM-Karte freischaltest, prüfe die Rufnummernmitnahme.

This means the same thing.

When the bevor-clause comes first, it is still a subordinate clause with the verb at the end:

• Bevor du die SIM-Karte freischaltest

Then the main clause follows:

• prüfe die Rufnummernmitnahme

This kind of reordering is very common in German.