Zítra začne aktivace SIM karty a přenos telefonního čísla.

Because Czech word order is flexible. Putting zítra first highlights the time: tomorrow.

A more neutral order is also possible: Aktivace SIM karty a přenos telefonního čísla začne zítra.

Both mean the same thing. Czech often moves time expressions to the front very naturally.

Because začne is from the perfective verb začít (to begin). In Czech, the present forms of perfective verbs usually have future meaning.

So:

• začíná = is beginning / begins (imperfective, present)
• začne = will begin (perfective, future meaning)

That is why začne is the correct form here for a one-time event happening tomorrow.

Good question. Many learners expect plural začnou, and that would also be possible.

Why singular appears here:

• the verb comes before the subject
• the two items are being presented as one combined process or service operation
• this kind of singular is quite common in administrative or technical messages

So:

• Zítra začne aktivace SIM karty a přenos telefonního čísla. = acceptable, common in service-style language
• Zítra začnou aktivace SIM karty a přenos telefonního čísla. = also understandable, and some learners may find it more logical

If the subject comes first, plural often feels more expected: Aktivace SIM karty a přenos telefonního čísla začnou zítra.

They are in the nominative singular.

They are the main nouns that function as the subject of the sentence:

• aktivace = activation
• přenos = transfer

Even though they name actions, they are nouns, not verbs.

Because aktivace is followed by the genitive case: activation of what?

So:

• SIM karta = nominative, SIM card
• SIM karty = genitive singular, of the SIM card

This is a very common Czech pattern with nouns that describe actions:

• aktivace účtu = activation of the account
• změna adresy = change of address
• kontrola dokladu = check of the document

For the same reason: přenos takes the genitive.

You can think of it as:

• přenos čeho? = transfer of what?
• answer: telefonního čísla = of the phone number

Both words change because the adjective must agree with the noun:

• telefonní číslo = nominative singular
• telefonního čísla = genitive singular

So:

• číslo → čísla
• telefonní → telefonního

Usually no. SIM is an abbreviation, and in this sentence it stays unchanged.

The noun karta is the part that declines:

• SIM karta
• SIM karty
• SIM kartě, etc.

So Czech treats SIM as an indeclinable modifier here.

Because Czech does not use articles like English does.

So:

• SIM karta can mean a SIM card or the SIM card
• telefonní číslo can mean a phone number or the phone number

Context tells you which meaning is intended. In this sentence, the meaning is clearly specific from the situation.

Yes, but it sounds a bit official or service-oriented. It is very natural in messages from mobile operators, websites, apps, or customer support.

In everyday spoken Czech, people might use a more verbal and personal version, for example: Zítra se začne aktivovat SIM karta a přenášet telefonní číslo. or Zítra vám aktivujeme SIM kartu a přeneseme telefonní číslo.

The original sentence uses a noun-heavy style that is very common in formal notices.

Yes. That is a very close structural translation.

A literal breakdown is:

• Zítra = tomorrow
• začne = will begin / begins
• aktivace SIM karty = activation of the SIM card
• a = and
• přenos telefonního čísla = transfer of the phone number

So the Czech structure is quite close to English here, even though the grammar behind it is different.