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. Otherwise carrier stores, the airport and big-box retailers sell prepaid SIMs. 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. Check the carrier's compatibility tool against your exact model.
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 of a few hundred dollars. Prepaid has no check, no contract and is usually cheaper for the same data.
OnlineWho: You
4
Consider an MVNO on the same towers
Mint Mobile, Visible, US Mobile and Google Fi resell capacity on AT&T, T-Mobile and Verizon. Same coverage for materially less; the trade is deprioritised data during congestion and lighter support.
Mobile appWho: You
5
Check coverage on the mountain roads if you plan to hike
This is genuinely the local caveat. Coverage in the Cascades — the Mountain Loop Highway, much of Snoqualmie and North Bend, and most trailheads — is absent. Download offline maps before every hike and tell someone your route, because you cannot rely on a signal to call for help.
Mobile appWho: You
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, which releases the number permanently.
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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

The US has no SIM registration at all.

Most countries in this app require passport registration to activate a SIM and several require biometrics. The US requires nothing for prepaid. Arriving from the Gulf, South Asia or Southeast Asia the absence of paperwork is genuinely disorienting.

Source: community-reported

Mountain coverage is the local safety issue, not the city coverage.

Seattle is a city where an enormous share of residents hike, and the Cascades have essentially no mobile coverage. People move here, adopt the outdoor culture quickly, and head into terrain where they cannot call for help. Download offline maps, carry the ten essentials, and leave a route plan with someone — this is standard practice here for a reason.

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 and usually costs less, so the workaround is also the better deal.

Source: community-reported

MVNOs use the same towers for meaningfully less.

Mint, Visible, US Mobile and Google Fi lease capacity from the big three. Coverage is identical; you give up priority during congestion and retail support. For a single line the saving is large and the compromise small.

Source: community-reported