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
Ask about a student or academic plan if you qualify
With this many universities, carriers here market student and academic discounts more aggressively than in most cities, and university IT departments often negotiate rates. If you are affiliated with an institution, check before signing anything.
OnlineWho: You
5
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, materially lower price; the trade is deprioritised data during congestion and thinner support.
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.
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 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 surprising.

Source: community-reported

The T's older tunnels are worse for coverage than newer systems.

Boston runs the oldest subway in America and underground mobile coverage is inconsistent, particularly on the Green Line's older sections. Download what you need before a commute rather than assuming continuous service — this is a sharper problem here than in most US cities.

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