Before you start

An unlocked handset, or an eSIM-capable one
A US address for postpaid, but not for prepaid
A payment method — prepaid accepts foreign cards, postpaid usually does not

Step-by-step

1
Activate an eSIM before flying, or buy prepaid on arrival
A US eSIM activates before you land so you have a working number immediately for rides, deliveries and bank verification codes. No identity registration is required at any point.
OnlineWho: YouDay 1
2
Check your handset is unlocked and band-compatible
Phones bought on contract abroad are frequently locked, and US band combinations trip up some regional models. With 3G shut down there is no fallback network to land on.
OnlineWho: You
3
Start prepaid rather than fighting a credit check
Postpaid runs a credit check. With no US file you will be declined or asked for a deposit. Prepaid has no check and is usually cheaper for the same data allowance.
OnlineWho: You
4
Register for the county's emergency notification system
Federal wireless emergency alerts reach every phone automatically, but Sacramento County's own notification system — used for evacuation orders, flood warnings and localised emergencies — requires you to opt in and register an address. Do this in week one. In a flood and fire region this is the alert that will be specific to your street rather than to the county.
OnlineWho: YouWeek 1
5
Keep the federal alerts on as well
Flood warnings, evacuation notices and extreme heat and air quality alerts arrive through the federal alert system. Some categories can be silenced in settings and people do silence them after one loud test. Leave the emergency categories on.
Mobile appWho: You
6
Add an air quality app before fire season
Late summer and autumn smoke is a recurring event here and the difference between a day you can run outdoors and one you cannot is a number. An air quality index app with push alerts is standard local equipment.
Mobile appWho: You
7
Port rather than cancel if you switch later
Number portability is a legal right and works between carriers and MVNOs. Request the port from the new carrier — never cancel the old service first, or you lose the number.
OnlineWho: You

Documents you’ll need

Passport for postpaid; nothing at all for prepaid
US address for postpaid
A payment card — prepaid usually accepts foreign cards, postpaid rarely does

Things most newcomers don’t know

The county alert system is opt-in, and it is the one that knows your street.

Federal wireless emergency alerts are automatic but coarse — they cover a broad area. Sacramento County's own notification system sends evacuation orders and flood warnings to registered addresses, which in a levee city and a fire region is the difference between a general warning and an instruction that applies to you. Almost no newcomer registers, because nothing prompts them to.

Source: Sacramento County / community-reported

Public safety power shutoffs are a Northern California fact of life.

Utilities de-energise lines during extreme fire weather. Inside the SMUD service area in the city this is far less common than in the investor-owned foothill territory, but if you live or work up towards Placerville or Auburn it is a real planning consideration. A power bank and a plan for a day without electricity are reasonable.

Source: community-reported

Air quality here is a number you should be able to see.

Wildfire smoke has repeatedly given Sacramento some of the worst readings in the world for days at a stretch. Unlike heat, you cannot judge it by feel once it is moderately bad. An AQI app with alerts turns a vague anxiety into a decision about whether to open the windows.

Source: community-reported

The US has no SIM registration at all.

Most countries in this app require passport registration to activate a SIM. The US requires nothing whatsoever for prepaid — you can buy one in a supermarket and be online in minutes.

Source: FCC — consumer guides