Before you start

A valid identity document: HKID card if you have one, otherwise your foreign passport (you'll sign a declaration that you don't hold an HKID)
An unlocked phone (Hong Kong phones are sold unlocked; eSIM is widely supported on recent iPhones and Androids)
For postpaid plans with autopay: usually an HKID plus a local credit card or Hong Kong bank account; a residential address helps but isn't always mandatory

Step-by-step

1
Pick prepaid vs postpaid (and decide if you even need a shop)
For your first weeks, a prepaid stored-value or data SIM is the path of least friction — csl, 1010, 3HK, China Mobile HK (CMHK) and SmarTone all sell them. Typical local prepaid data SIMs run HK$50-100 for several GB to multi-day unlimited 5G. If you're staying long-term and already hold an HKID, a postpaid plan (HK$100-300/mo) gets you more data, a stable number, and roaming. eSIM is supported by all four carriers for postpaid and many prepaid products — convenient, but you still must complete real-name registration.
In personWho: YouSame dayPrepaid SIM HK$50-100 (~US$6-13); postpaid HK$100-300/mo (~US$13-38)
2
Buy the SIM — 7-Eleven, Circle K, vending machines, or a carrier shop
Prepaid SIMs are sold everywhere: 7-Eleven and Circle K stock csl/CMHK/3HK cards, there are SIM vending machines at the airport and MTR stations, and every carrier has retail shops in malls. Convenience-store cards are blank until you register and activate them. For postpaid or anything needing a credit check, go to a carrier shop (csl/1010, 3HK, CMHK, SmarTone) or order online — you'll show your HKID and a payment method there.
In personWho: You15-30 minCard price only
3
Complete MANDATORY real-name registration before activation
This is the non-negotiable step. Every SIM (prepaid and postpaid) must be registered to an identity document via the carrier's app or registration website before service turns on. HKID holders can register through 'iAM Smart' or by uploading an HKID copy. If you don't have an HKID yet, you register with your foreign passport and tick a declaration stating you don't hold an HKID — this is explicitly allowed. The cap: an individual may register at most 10 prepaid SIMs per operator.
Mobile appWho: You (via carrier app / website / iAM Smart)5-15 min; activation usually instant to a few hoursFree
4
Set up home broadband (optional but cheap and fast)
Order 1000Mbps fibre from HKBN, Netvigator (HKT/PCCW), China Mobile HK or i-Cable/HGC for roughly HK$130-230/month on a 12-24 month contract (list prices look higher; the real promo rates are far lower — compare via a quote service or negotiate). Many Hong Kong flats are pre-wired, so installation can be fast — sometimes self-install with a posted router, otherwise a technician visit within days. Speeds are famously high.
OnlineWho: You + ISP technician (if wiring needed)A few days to ~2 weeks for a technician slot~HK$130-230/mo (~US$17-30); installation often waived on contract

Documents you’ll need

HKID card (if held) — or foreign passport plus a signed 'no HKID' declaration
Date of birth and ID number (required fields for real-name registration)
For postpaid/autopay: local credit card or Hong Kong bank account details
Residential address (typically needed for home broadband install)

Things most newcomers don’t know

The 'anonymous Hong Kong prepaid' you may have read about no longer exists — every SIM must be registered to an ID before it works.

Under the Telecommunications (Registration of SIM Cards) Regulation, real-name registration became mandatory for prepaid SIMs from 1 March 2022. Buying a blank card at 7-Eleven is still easy, but it stays dead until you register it. Budget five extra minutes for the app step.

Source: OFCA — Real-name Registration Programme for SIM Cards

You can get a fully working local SIM on your passport alone — you don't have to wait for your HKID.

OFCA explicitly accepts foreign passports for registration, with a declaration that you don't hold an HKID. New arrivals can have a Hong Kong number on day one rather than waiting weeks for the HKID. (Postpaid plans with autopay are where the HKID/bank requirement usually bites.)

Source: OFCA — Real-name Registration FAQ

Don't pay the broadband 'list price' — the real rate is often less than half.

Carriers like Netvigator publish list prices (e.g. ~HK$698/mo for 1000M) but actual contract/promo rates for 1000Mbps land around HK$130-230/mo, and pricing varies by building. Use a comparison/quote service or negotiate at signup; pre-wired flats also mean a faster, sometimes free, install.

Source: Netvigator / HKBN plan pages

Common mistakes to avoid

Assuming a convenience-store SIM works straight out of the pack — it won't activate until real-name registration is complete
Hitting the 10-prepaid-SIMs-per-operator cap if you churn through cards; spread registrations across carriers or use postpaid
Trying to register a prepaid SIM with no acceptable ID on hand — have your passport or HKID ready before you start the app flow
Letting a prepaid stored-value SIM lapse — miss the top-up window and the number/balance can be forfeited
Signing a broadband contract at the headline list price instead of the promo rate, or locking into 24 months in a short lease