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. No identity registration is required at any point, for either option.
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.
OnlineWho: You
4
Check the FCC broadband map before signing a lease
Boise's older core, the Bench and the post-2000 subdivisions west of town were built out at different times by different providers, and availability changes address by address. The FCC's national map reports at address level and is free.
OnlineWho: YouBefore signing a lease
5
Assume no signal past the trailhead
The foothills start at the top of the street in the North End and coverage falls away quickly beyond the first ridge, and further out in the Sawtooths and the Owyhees there is none at all. Download offline maps, tell someone your route, and consider satellite SOS if you hike alone.
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, or the number is gone.
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 wilderness starts at the end of the street, and so does the dead zone.

Boise's selling point is that trailheads are walkable from residential neighbourhoods. The corollary is that people go further and higher than they intended on a weekday evening, in terrain where coverage disappears after the first ridge. Offline maps and a route left with someone are standard local practice, not paranoia.

Source: Ridge to Rivers — trail system

Check the address, not the city, for broadband.

The FCC's map reports availability at address level. Boise's pre-war core, the Bench and the newer west-side subdivisions were built out separately, so two flats a mile apart can have completely different options. This is the cheapest pre-lease check available and almost nobody does it.

Source: FCC — national broadband map

Leave weather alerts on through fire season.

The National Weather Service office in Boise issues red flag warnings and evacuation-relevant alerts through a long fire season, and Wireless Emergency Alerts arrive on any US handset with no signup. In a state where fires move fast through sagebrush and canyon country, that is the fastest warning available.

Source: National Weather Service — Boise

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, which makes arriving with a working local number the easiest administrative task of the whole move.

Source: FCC — consumer guides