Before you start

A passport or ID (required by Portuguese law to register any SIM, prepaid included)
An unlocked phone, or an eSIM-compatible device for an eSIM
For a postpaid contract or fibre bundle: a NIF (tax number) and usually a Portuguese bank account (IBAN) for direct debit (débito direto)
A Portuguese address — needed for a contract/fibre, not for prepaid

Step-by-step

1
Choose your fork: prepaid now, contract later
Prepaid (pré-pago) is the fast, no-commitment route — top up as you go, no NIF or bank account, just a passport. A postpaid contract (pós-pago) is cheaper per GB and can bundle home internet/TV, but generally requires a NIF plus a Portuguese IBAN for direct debit. Almost every newcomer starts prepaid and switches once a NIF and bank account are in place.
OnlineWho: YouA few minutes to decideFree (decision)
2
Buy and register a prepaid SIM or eSIM
Buy at a MEO/NOS/Vodafone store, FNAC/Worten, supermarkets (Continente, Pingo Doce), or kiosks, or activate an eSIM from the carrier app. Portuguese law requires SIMs to be registered to an identity, so the seller records your passport at purchase — keep ID handy even for a cheap SIM. For cheap calls home, Lycamobile and Lebara (both on Vodafone's network) are the go-to MVNOs; Uzo (MEO) has very cheap data top-ups.
In personWho: You (carrier store, kiosk, or app)Same day; 15-30 minutes in store, minutes for an eSIMPrepaid starter packs roughly €10-15 with initial data
3
Switch to a postpaid plan and port your number
Once you have a NIF and a Portuguese bank account, move to a monthly plan (often €10-15/month for generous data + unlimited national/EU calls). Keep your number for free via portability: the new operator handles it using your CVP code, and the switch completes within one business day with at most a short outage. Budget youth brands Moche/WTF (NOS) and Yorn (Vodafone) offer cheaper tiers.
In personWho: You (with the new carrier; provide NIF + IBAN)Same day to sign up; portability within ~1 working dayPostpaid plans roughly €10-20/month; SIM swap usually free
4
Set up home internet (fibra) as a bundle
Porto has near-universal fibre. Order a 'pacote' from MEO, NOS, Vodafone, or budget players DIGI/NOWO — needs a NIF, your address, and an IBAN for direct debit. Standalone 1 Gbps fibre runs ~€30/month; net+TV+mobile bundles ~€55/month. Almost all carry a 24-month fidelização (lock-in); DIGI and low-cost brands offer ~€10-15 fibre with only a 3-month lock-in. An installation appointment is scheduled (often a few days to ~2 weeks out).
OnlineWho: You (online, carrier store, or phone; then a technician visit)Sign-up same day; install appointment typically a few days to ~2 weeksFibre ~€30/month standalone; bundles ~€39-55/month; install often waived on 24-month deals

Documents you’ll need

Passport or ID card (for SIM registration — prepaid and postpaid)
An unlocked or eSIM-compatible phone
NIF (Portuguese tax number) — for any contract or fibre bundle
Portuguese bank account / IBAN — for postpaid and fibre direct debit
Proof of address — for a fibre/home-internet contract
CVP (Código de Validação da Portabilidade) — when porting your number

Things most newcomers don’t know

Postpaid is gated by two things newcomers don't have on day one: a NIF and a Portuguese IBAN for direct debit. Start prepaid, then port your number once both are sorted.

Saves a wasted shop trip — carriers will turn you away from a contract without a NIF and bank account, but prepaid needs only a passport, so you're connected immediately and lose nothing by switching later.

Source: Carrier prepaid vs. postpaid terms (MEO/NOS/Vodafone)

A Portuguese SIM 'roams like at home' across the entire EU/EEA at no extra cost — one Porto prepaid SIM covers trips to Spain, France, etc.

No need to buy separate SIMs for EU travel; data/calls use your home allowance (subject to a fair-use cap), which matters for cross-border living in Iberia.

Source: EU Roam Like At Home rules; ANACOM

Operators cannot refuse to port your number just because you're mid lock-in — but you still owe the early-termination penalty to the old provider.

You can always keep your number when switching, yet leaving a 24-month fibre/postpaid contract early still costs you — so weigh the fidelização before signing the cheapest bundle.

Source: ANACOM — number portability & contract rules

Common mistakes to avoid

Signing a 24-month fidelização for the headline price, then paying a steep early-termination penalty if you move flat or leave Portugal — budget brands (DIGI, Uzo) offer 3-month lock-ins instead
Assuming you can get a postpaid contract on arrival: most require a NIF and a Portuguese bank account for direct debit
Forgetting to register/identify the SIM correctly — an unregistered SIM can be deactivated under Portuguese rules
Booking fibre and expecting same-day internet — an installation/technician appointment is scheduled and can be days to weeks out
Letting a prepaid SIM go dormant — no top-up/usage for several months can deactivate the number and lose it

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