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, both airports and big-box retailers sell prepaid SIMs. 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.
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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 of a few hundred dollars. Prepaid has no check and is usually cheaper for the same data.
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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.
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5
Check underground L coverage on your line
The CTA has cellular service in the subway tunnels, but quality varies by carrier and by segment. If you commute on the Red or Blue Line's underground sections, this is worth checking before you commit to a carrier.
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.
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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.

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

Cold destroys phone batteries faster than you expect.

At -15°C a phone can drop from 40% to nothing in minutes and shut down outdoors. In a city where you wait for buses in February, keep the phone in an inside pocket rather than an outer one, and carry a power bank. People learn this by being stranded once.

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.

Source: community-reported