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
The metro spans three counties and several decades of construction — the peninsula's historic blocks, mid-century West Ashley, the 1990s James Island sprawl and the new master-planned communities in Berkeley County all have different options. The FCC's national map reports at address level and is free.
OnlineWho: YouBefore signing a lease
5
Leave Wireless Emergency Alerts on, and add the county's system
WEA arrives on any US handset with no signup and carries evacuation orders, tornado warnings and flash flood warnings. Charleston, Berkeley and Dorchester counties each run their own opt-in notification system on top, which is where the zone-specific detail lives. Sign up for the county you actually live in.
Mobile appWho: YouWeek 1
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 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 on mobile service

Check the address, not the city, for broadband.

The FCC's map reports availability at address level. Charleston's housing stock spans three centuries and three counties, and two flats a mile apart can have completely different options — a converted single house on the peninsula and a 2024 build in Nexton are not the same market. This is the cheapest pre-lease check available and almost nobody does it.

Source: FCC — National Broadband Map

Alerts are the difference between evacuating and being told to.

South Carolina orders coastal evacuations by lettered zone and reverses the I-26 lanes when it does. Wireless Emergency Alerts reach every handset without a signup, and the county systems carry the zone detail. In a storm the difference between leaving early and leaving late is measured in hours on a contraflowed interstate.

Source: FCC — wireless emergency alerts

Keep a plan for when the power goes and the tower does not.

Tropical systems take out grid power for days across the Lowcountry while cell sites run on backup that eventually runs out. A charged power bank, a downloaded offline map and one out-of-state contact everyone in the household knows to call are the standard local preparations, and they cost nothing.

Source: Ready.gov — hurricanes and evacuation planning