jungyohan yeonrakcheoneun memojange jeogeo duseyo.

적어 두세요 means please write it down and keep it that way for later.

The pattern -아/어 두다 adds the idea of doing something in advance or leaving it done for future use.

So:

• 적으세요 = write it down
• 적어 두세요 = write it down and have it ready/saved for later

In this sentence, that nuance is important because contact information is something you may need later.

Because 적다 and 두다 are separate verbs.

• 적다 = to write down
• 두다 = to put, leave, keep

In grammar, -아/어 두다 combines with another verb to mean do something in advance and leave it done. Even though it works like one grammar pattern, it is often written with a space because 두다 is still originally a separate verb.

You may also sometimes see forms like 적어두세요 in less strict writing, but 적어 두세요 is the standard spacing.

는 is the topic particle.

Here, 중요한 연락처는 means something like:

• as for important contact information
• important contacts, (you should...)

It sets important contact information as the topic of the sentence.

Why not 를?
Because the sentence is not simply focusing on the object of write. Instead, it sounds more like giving advice about that topic:

• As for important contacts, write them down in your memo pad.

This is very natural in instructions or advice.

Here 에 marks the place/location where the writing goes.

So:

• 메모장에 적다 = to write in/on a memo pad

In Korean, 에 is commonly used with verbs to show the location where something is written, placed, or exists.

Examples:

• 공책에 쓰다 = write in a notebook
• 벽에 붙이다 = stick onto the wall
• 종이에 적다 = write on paper

So 메모장에 means in/on the memo pad.

It can be either singular or plural, depending on context.

Korean nouns usually do not have to show singular vs. plural explicitly. So 연락처 can mean:

• a contact detail
• contact information
• contacts

In this sentence, it often feels natural to understand it as important contact information or important contacts in general.

If the speaker wanted to emphasize plural, they could say 연락처들, but Korean often leaves that unmarked.

연락처 means contact information or contact details.

It can include:

• a phone number
• an email address
• other ways to reach someone

So it is broader than just phone number.

For comparison:

• 전화번호 = phone number specifically
• 연락처 = contact info/contact details more generally

중요한 is the noun-modifying form of 중요하다.

• 중요하다 = to be important
• 중요한 연락처 = important contact information / important contacts

When a descriptive verb (often called an adjective in Korean learning materials) comes before a noun, it changes form:

• 크다 → 큰 집
• 좋다 → 좋은 사람
• 중요하다 → 중요한 연락처

So 중요한 is just the form used before the noun 연락처.

두세요 is a polite, honorific request/instruction form.

Breaking it down:

• 두다 = to leave/keep
• 두세요 = please leave/keep; please do so

In this sentence, the whole ending sounds like a polite instruction:

• suitable for announcements
• advice
• instructions
• polite everyday speech

It is softer and more polite than a plain command.

Compare:

• 적어 둬. = write it down and keep it (casual)
• 적어 두세요. = please write it down and keep it (polite)
• 적어 두십시오. = please write it down and keep it (more formal)

Yes, that is a very natural translation.

Even if the Korean literally includes memo pad and write it down, in natural English you could translate it in several ways depending on context:

• Write down important contact information in your memo pad.
• Make a note of important contacts.
• Be sure to write down important contact details.

The exact English wording can change, but the Korean nuance of record it for future use should be preserved.

It can mean both, depending on context.

메모장 literally suggests a memo pad/notepad, but in modern usage it can also refer to a notes app or digital notepad.

So this sentence could mean:

• write important contacts in a physical memo pad
• save them in a notes app

The surrounding situation would tell you which one is meant.

Yes, you can, and it is grammatically correct.

The difference is mainly in focus:

• 중요한 연락처는 메모장에 적어 두세요.
  = As for important contacts, write them down in your memo pad.
  This sounds like advice about that topic.

• 중요한 연락처를 메모장에 적어 두세요.
  = Write the important contact information in your memo pad.
  This focuses more directly on the object being written.

Both are natural, but 는 often feels especially natural for general advice or reminders.

A casual version could be:

• 중요한 연락처는 메모장에 적어 둬.

If speaking even more softly to a friend:

• 중요한 연락처는 메모장에 적어 둬야 해.
  = You should write down important contacts.

The original 적어 두세요 is the polite version, which is more appropriate for instructions, announcements, or speaking respectfully.

In careful pronunciation, it is close to:

• 저거 두세요 is not correct
• 적어 두세요 is roughly jeo-geo du-se-yo in romanization terms, but that can be misleading

More usefully:

• 적어 comes from 적다
• In real speech, 적어 often sounds close to 저거 to learners, but it is still the verb 적다

So the whole phrase may sound somewhat like:

• 저거 두세요 to an untrained ear

But the actual form is:

• 적어 두세요

This is a common thing in Korean: conjugated forms can sound different from what learners expect if they only know the dictionary form.