Before you start

Passport, for a prepaid SIM
NIE and a Spanish bank account, for a contract
An unlocked or eSIM-capable handset
A Spanish address, for fibre installation

Step-by-step

1
Buy a prepaid SIM on your passport on arrival
Available at the airport, phone shops and supermarkets. Registration against your passport is required by law and takes a few minutes at the counter. A Spanish number in your first hour unlocks bank verification and appointment systems.
In personWho: YouDay 1
2
Wait for the NIE before taking a contract
Contract tariffs need a NIE and usually a Spanish IBAN for the direct debit. They are considerably better value than prepaid and typically bundle mobile with fibre, but there is no way to shortcut the identity requirement.
In personWho: You
3
Bundle fibre with mobile, which is how Spain prices it
Spanish operators price convergent bundles aggressively and mobile alone is poor value by comparison. Fibre coverage in Seville is good and speeds are high by European standards, so the bundle is usually the right answer.
OnlineWho: You
4
Consider the low-cost operators seriously
Virtual operators reselling the main networks are substantially cheaper and use the same masts. For a newcomer without a credit history they are also more willing to take a customer on a passport plus NIE without extensive checks.
OnlineWho: You
5
Keep your number when you switch
Portability between Spanish operators is a legal right, handled by the receiving operator within a short statutory period. Never cancel first — you lose the number.
OnlineWho: You
6
Check the risers in old-city buildings before assuming fibre
Getting fibre into a building in Santa Cruz or the older parts of Triana depends on the existing risers and sometimes on the building community's agreement. Two flats on the same lane can have very different options. Ask what is already installed before signing a lease if a fast connection is load-bearing for your work.
OnlineWho: You

Documents you’ll need

Passport, for prepaid registration
NIE and Spanish IBAN, for a contract
Proof of address, for fibre

Things most newcomers don’t know

There is no anonymous SIM in Spain, unlike the UK.

Every Spanish SIM must be registered against an identity document at activation. A passport is enough for prepaid, so this is not a barrier — but arriving expecting to buy a SIM off a supermarket shelf and use it immediately, as in Britain, means an unexpected counter visit with documents in hand.

Source: Ministerio para la Transformación Digital

The NIE, not the money, is what gates a good tariff.

Contract plans are far better value than prepaid and almost always bundle fibre, but they require a NIE and usually a Spanish IBAN. There is no premium you can pay to skip this. Plan on several weeks of prepaid while the residency paperwork completes, and treat that as part of the cost of the move.

Source: community-reported

Spanish fibre is genuinely excellent and cheap, which surprises people.

Spain has among the highest full-fibre coverage in Europe, well ahead of Germany or the UK, because the incumbent and its competitors overbuilt aggressively. Symmetric gigabit connections are ordinary and inexpensive. For remote workers this is one of the strongest and least advertised practical arguments for the country — and it is what makes Seville's low rents actually usable.

Source: Comisión Nacional de los Mercados y la Competencia

Heat affects equipment as well as people.

A flat that reaches the high thirties indoors in August will throttle a laptop and shorten the life of a router left in direct sun. Remote workers here routinely move the router out of a west-facing window and work in the coolest room rather than the nicest one. It sounds trivial until a work machine starts thermally throttling in the middle of a call.

Source: community-reported

Common mistakes to avoid

Expecting to buy an anonymous SIM as in the UK.
Signing a long contract before you have a NIE and being pushed onto a worse tariff.
Buying mobile alone when Spain prices convergent bundles far better.
Cancelling your old service before porting the number.
Assuming fibre is available in an old-city building without checking the risers.

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