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
Turn on Wireless Emergency Alerts and register for county alerts
Wildfire evacuation warnings and orders reach you through the federal alert system and through Orange County's own emergency notification service, which you have to opt into with your address. In the eastern villages at the wildland interface, that registration is not optional in any practical sense. Do it in week one.
Mobile appWho: YouWeek 1
5
Enable earthquake early warning
California operates a public earthquake early warning system that pushes an alert to phones in the seconds before shaking arrives — enough time to drop, cover and hold on. It is built into recent phone operating systems and there are dedicated apps as well. Check it is switched on rather than assuming, and know that the warning is seconds, not minutes.
Mobile appWho: YouWeek 1
6
Know your evacuation route out of the eastern villages
Portola Springs, Orchard Hills and the upper edges of the city have limited road connections out toward the 241 and the 133. In a fast-moving Santa Ana fire, everyone leaves at once. Look at the map before September and decide which way you would go — this is the specific local version of the general advice.
In personWho: You
7
Check broadband by address, not by village
Use the FCC's National Broadband Map for the specific street address before signing. Irvine's fibre coverage is good in much of the city and uneven in places, and the newer Great Park villages and the older 1970s ones are not the same picture. For a hybrid or remote job this is a working requirement.
OnlineWho: You
8
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

Two hazards, two completely different warning windows.

A wildfire evacuation may give you hours if you are registered for county alerts and minutes if you are not. An earthquake gives you seconds, and only if early warning is enabled on the phone. They need different preparation and people who set up for one assume they have covered the other.

Source: community-reported

California's earthquake early warning is real and it is on your phone already.

The statewide public alerting system pushes a warning in the seconds between a quake starting and the shaking reaching you. Newer phone operating systems support it natively. Seconds sound useless until you have used them to get away from a window — and it costs nothing to switch on.

Source: community-reported

The United States 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

Check fibre at the address, not the village.

Irvine was built in phases over fifty years and the telecoms infrastructure reflects that, so a 1970s village and a 2020s one are not the same proposition. The FCC's map is address-level and free; a leasing office's 'high-speed internet available' is neither specific nor binding.

Source: FCC — National Broadband Map

Common mistakes to avoid

Never registering for county emergency alerts while living at the wildland interface.
Leaving earthquake early warning switched off because you did not know it existed.
Applying for postpaid with no credit file and facing a large deposit.
Bringing a carrier-locked handset from abroad and discovering it on arrival.
Assuming fibre is available because a neighbouring village has it.
Cancelling the old carrier before requesting the port, and losing the number.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.