Before you start

Unlocked handset
Passport or identity card for mandatory registration
Swiss address and bank account for a postpaid contract

Step-by-step

1
Buy a prepaid SIM the day you land
Available at the airport, in Migros and Coop and in operator shops. Registration against your passport is a legal requirement, so bring it.
In personWho: YouCommonly CHF 10–30 including credit
2
Look at the discount brands before the flagship ones
Wingo runs on Swisscom, Yallo on Sunrise, and M-Budget and Coop Mobile on the main networks too. Same coverage, substantially lower price, usually without a long contract.
OnlineWho: You
3
Turn off automatic network selection near the border
In Geneva the French networks are often the strongest signal indoors. Manually locking to a Swiss operator prevents a domestic call becoming an international roaming charge without you touching anything.
Mobile appWho: You
4
Move to postpaid once you have an address and a bank account
Contracts need both, and sometimes a permit. Prepaid is the bridge, not a compromise.
OnlineWho: You
5
Choose a plan that explicitly covers France if you cross regularly
Anyone shopping, hiking or living on the French side needs EU data written into the plan. Most Swiss plans include some EU allowance now, but the amounts vary sharply.
OnlineWho: You

Documents you’ll need

Passport or identity card
Swiss address for postpaid
Swiss bank account for direct debit

Things most newcomers don’t know

Accidental roaming onto French networks is a real and recurring Geneva bill.

The canton has 103 km of French border and only 4.5 km of Swiss. In Meyrin, Vernier, Carouge and Thônex a French mast is frequently the strongest signal indoors. With automatic network selection on, your phone can spend a whole evening roaming while you sit in Switzerland. Lock the network manually.

Source: community-reported, consistently

EU roaming rules do not apply to Switzerland in either direction.

An EU SIM roams here at non-EU rates, and a Swiss SIM in France can be expensive unless the plan says otherwise. People who move from an EU country and keep their old number for a few months are the ones who get the four-figure bill.

Source: Switzerland's non-EU status under the roaming regulation

The cheap brands are the expensive networks wearing a different name.

Wingo is Swisscom, Yallo runs on Sunrise. The masts, the coverage and the speeds are the same; only the customer service tier and the price differ. In one of the most expensive telecom markets in Europe this is one of the few savings available without a trade-off.

Source: community-reported, widely corroborated

SIM registration against an identity document is compulsory and enforced.

Switzerland does not sell anonymous prepaid SIMs. Buying one without ID is not possible, and a SIM registered to someone else creates problems later when you try to port the number to a contract in your own name. Register it correctly on day one.

Source: OFCOM — telecommunications regulation

Common mistakes to avoid

Leaving automatic network selection on and roaming onto a French mast from your Swiss flat.
Assuming EU roam-like-at-home covers Switzerland.
Signing a 24-month flagship contract without checking the discount brand on the same network.
Buying a postpaid plan before you have an address and a bank account.
Registering the SIM in a colleague's name and then being unable to port the number.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.