Learn Hardcore Indonesian: Tolong kirim nomor telepon Anda sebelum rapat dimulai. - Please send your phone number before the meeting starts.

Tolong = “please (help by doing this).” It’s a polite, neutral request, common in speech and writing.
Mohon = more formal/requestive, often in notices or business: Mohon kirim…
Harap = impersonal/official: Harap kirim… (sounds like a posted instruction)
Silakan = “please go ahead,” gives permission/invites: Silakan kirim…
Bisa…?/Bisakah…? = soft question-request: Bisa kirim…? / Bisakah Anda mengirim…?
Boleh…? = asks permission/soft request: Boleh minta nomor teleponnya?

Why is the verb in the bare form kirim? How is it different from kirimkan, mengirim, and mengirimkan?

kirim = bare root used for imperatives/requests: “send.”
kirimkan = imperative with -kan; slightly more formal; often used when you also mention the recipient: Kirimkan nomor… ke saya.
mengirim = active verb (“to send”) for statements: Saya mengirim email.
mengirimkan = like mengirim, often focuses on the item sent or formality: Saya mengirimkan berkas itu. In your sentence, kirim or kirimkan are both fine.

Do I need to say who to send it to (e.g., “to me”)? The sentence doesn’t have a recipient.

Not strictly, if the context is clear. If you want to be explicit:

Tolong kirim nomor telepon Anda ke saya…
More formal: …kepada saya…
To a group/place: …ke grup, …ke email ini, …lewat/ melalui WhatsApp.

Is Anda the best pronoun here? What about kamu, Bapak/Ibu, Mas/Mbak?

Anda = polite, neutral, common in customer-facing writing and formal emails. Rare in casual face-to-face talk.
kamu = informal/equal or younger.
Bapak/Ibu = very polite to an older/respected person (Mr./Mrs./Sir/Ma’am).
Mas/Mbak = polite and friendly (esp. Java/urban), roughly “sir/ma’am” to a young adult. Choose based on relationship and setting.

Does Anda have to be capitalized?

Style guides recommend capital Anda as a respectful second-person pronoun in formal contexts. In casual texting you’ll see lowercase anda, but capitalizing is safer/formal.

Could I drop Anda and just say “Tolong kirim nomor telepon…”?

You can, but it becomes ambiguous (“a phone number” rather than “your phone number”). Clearer options:

Tolong kirim nomor telepon Anda…
To be polite without a pronoun: Tolong kirim nomor telepon Bapak/Ibu…
Very colloquial/contextual: Tolong kirim nomor teleponnya… (-nya relies on context to mean “your”/“that” number.)

Is nomor telepon the normal way to say “phone number”? What about HP/WA/ponsel? Any spelling gotchas?

nomor telepon = standard “phone number.”
nomor HP (handphone) / nomor ponsel = mobile number.
nomor WA = WhatsApp number (common in practice). Spelling:
Standard: telepon (not “telefon”); nomor (informal “nomer” exists but is nonstandard).
Abbreviations you’ll see: No. HP, no. telp. (informal/office notes).

Why is it sebelum rapat dimulai instead of sebelum rapat mulai? Are both correct?

Both are correct, with a nuance:

sebelum rapat dimulai = passive “before the meeting is started” (slightly more formal/impersonal).
sebelum rapat mulai = intransitive “before the meeting starts” (simple/natural). You can also say: sebelum rapatnya mulai (specific meeting), or sebelum kita mulai rapat (agent “we” present).

What does the prefix di- in dimulai do? Is it the same as the preposition di?

di- (no space) is the passive verb prefix: dimulai = “is started.”
di (with space) is the location preposition: di kantor = “at the office.” Never write di mulai here; it must be dimulai.

Could I say sebelum kita mulai rapat instead?

Yes. Variants:

sebelum kita mulai rapat
sebelum kita memulai rapat (more formal/explicit transitive) These shift focus to the agent (“we”) starting the meeting.

Do I need akan to mark the future (e.g., sebelum rapat akan dimulai)?

No. Indonesian doesn’t require tense marking. sebelum rapat dimulai already implies a future-relative event. You might add nanti for emphasis, but it’s optional.

Can I move the time clause to the front: “Sebelum rapat dimulai, tolong kirim…”?

Yes. Both orders are natural:

Tolong kirim … sebelum rapat dimulai.
Sebelum rapat dimulai, tolong kirim … (slight emphasis on the time condition).

How formal is the original sentence? Can you give formal and casual alternatives?

Original is neutral–polite.
More formal: Mohon nomor telepon Anda dikirim sebelum rapat dimulai.
Neutral: Silakan kirim nomor telepon Anda sebelum rapat dimulai.
Casual: Bisa kirim nomor HP/WA kamu sebelum rapat mulai?
Very casual/request: Boleh minta nomor WA-nya sebelum rapat mulai?

Should I add -lah (kirimlah) to sound polite?

Usually no. -lah can soften imperatives in formal/literary style, but with Tolong it can feel redundant or stiff. Tolong kirim… is already polite.

What’s the difference between rapat, pertemuan, and (loanword) meeting?

rapat = a formal/business/organizational meeting (agenda, minutes).
pertemuan = any meeting/encounter; broader and slightly more formal-sounding.
meeting = English loan; common in office slang, less formal. Your clause works with any: sebelum rapat/pertemuan/meeting dimulai.

Is there a more “impersonal notice” style?

Yes, passive/impersonal is common:

Harap nomor telepon Anda dikirim sebelum rapat dimulai.
Mohon nomor telepon Anda dikirim sebelum rapat dimulai. These read like announcements/instructions.

How do -kan and -i differ with “send,” and can I use them here?

With the base kirim:

mengirimkan [thing] (kepada) [recipient]: focuses on the item sent.
- Example: Tolong kirimkan nomor telepon Anda kepada saya…
mengirimi [recipient] [thing]: focuses on the recipient.
- Example: Tolong mengirimi saya nomor telepon Anda… For imperatives, kirim/kirimkan are both fine; pick the one that matches your focus or tone.

Any small add-ons to soften the tone in speech?

You can add sentence-final particles:

…ya. (soft, friendly)
…dong. (colloquial, persuasive) Example: Tolong kirim nomor telepon Anda sebelum rapat dimulai, ya.