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 for the taxi, the landlord and the bank. No identity registration is required at any point.
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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.
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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.
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4
Leave Wireless Emergency Alerts switched on
WEA is how tornado warnings and flash-flood warnings reach handsets, and it is on by default. People disable it because a late-night test is annoying and then miss the one that matters. It is the only alert that will wake you.
Mobile appWho: YouBefore March
5
Know the difference between a watch and a warning
A watch means conditions are favourable across a large area and can last hours. A warning means a tornado has been detected in a specific place and you should already be moving to an interior room or basement. Newcomers routinely treat the two as the same thing.
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6
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 the number is gone.
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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

Outdoor sirens are not an indoor warning system, whatever people assume.

St. Louis area sirens are designed to be heard outdoors. They are not reliably audible inside a modern insulated building, let alone with the air conditioning running or while you are asleep. Wireless Emergency Alerts on your phone are the warning that will actually reach you, which is why turning them off is a genuinely dangerous convenience.

Source: community-reported

A warning gives you minutes, not hours.

Average tornado warning lead time in this region is measured in single-digit minutes. Working out where the basement or interior room is on the day you move in, rather than during the warning, is the whole preparation. Keep shoes and a torch there.

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, so day-one connectivity is one of the easiest parts of arriving.

Source: community-reported

The credit check is the barrier, not the documentation.

Carriers check credit before offering postpaid, and a newcomer with no file gets declined or charged a deposit. Prepaid sidesteps it entirely and usually costs less for the same allowance.

Source: community-reported