Before you start

The passport you entered on, for SIM registration and customs device registration
An unlocked handset and its IMEI, from *#06#
Your entry stamp or e-visa, for the customs registration
Address proof and usually a KITAS for a home fibre contract or postpaid line

Step-by-step

1
Buy the SIM in town rather than at the airport
Telkomsel GraPARI, Indosat, XLSMART and Tri all have staffed outlets in Yogyakarta's malls and along the main university roads. Bring your passport so the clerk completes registration on the spot. Yogyakarta International Airport is 40 kilometres west of the city, so you are unlikely to be buying there anyway.
In personWho: You15–20 minutes; live within the hourA generous monthly package is a low six-figure rupiah sum
2
Register the SIM against your passport and check it
An unregistered line does not activate. There is a cap on lines per identity per operator, so do not let a shop register spare numbers against your passport. Confirm the number is registered to your details before you leave.
In personWho: You, with the store filing itImmediate
3
Register your handset's IMEI with customs
A foreign-bought phone works for roughly 90 days then goes dark at device level. Register at the Bea Cukai desk on arrival — free below a value threshold, and considerably more expensive later when duty on the full value can be assessed. If you fly into Jakarta or Surabaya first, do it there rather than assuming you can sort it in Yogyakarta afterwards.
In personWho: You, at airport customsAbout 30 minutes on arrivalFree below the threshold; import duty above it or if late
4
Check what internet the room or house already has
This is a student city and a very large share of rental rooms and houses already have fibre installed and included in the rent — ask which provider, what the advertised speed is, and how many people share it, because a kos with twenty rooms on one connection is not a working-from-home proposition. In a standalone house, IndiHome, Biznet and others install within days to a couple of weeks.
In personWho: You, with the landlordDays to weeks if not already installedRoughly IDR 250,000–600,000 a month if you contract it yourself
5
Keep a data SIM on a second network
Shared student connections are congested in the evenings and power cuts take the router with them. A cheap data-only SIM on another operator turns an outage into an inconvenience. In a city where a lot of people work remotely on cheap rent, this is standard practice.
Mobile appWho: YouInexpensive

Documents you’ll need

Passport photo page, for SIM registration and customs device registration
Entry stamp or e-visa, for the IMEI registration
Handset IMEI from *#06#
KITAS and address proof, for a postpaid line or your own fibre contract

Things most newcomers don’t know

The 90-day cut-off is tied to your handset, so buying another SIM will not revive a dead phone.

Indonesia blocks unregistered foreign devices at the IMEI level. It presents as the phone losing all networks around three months in, and the instinctive fix — a new SIM — fails identically. The remedy is customs registration of the device, free on arrival and potentially expensive afterwards.

Source: Bea Cukai (Indonesian Customs) IMEI registration

'Wifi included' in a student city usually means a shared connection, and it matters which.

Kos rooms and shared houses here very often include internet, which is genuinely generous and genuinely variable — one fibre line shared by twenty rooms behaves nothing like a private connection at eight in the evening. Ask how many rooms share it and test it at the hour you would actually be working, not at midday when the building is empty.

Source: Practitioner reporting from Yogyakarta's rental market

The Telkomsel premium is worth it here only if you leave the urban area.

All four operators cover the city, Sleman and Bantul well. Telkomsel's real advantage is reach into Gunungkidul, the southern coast and the rural south — which matters a great deal if you do fieldwork or ride out at weekends, and not at all if your life happens between the university belt and Malioboro. Decide on where you will actually be.

Source: Operator coverage maps

Do not let a shop register spare lines against your passport.

One identity may register only a limited number of prepaid lines per operator. Shops sometimes add numbers against a customer to clear stock or hit a target, which consumes your allocation and leaves lines registered to you that you do not control. Check before you leave the counter.

Source: Indonesian SIM registration rules (Komdigi)

Common mistakes to avoid

Assuming a foreign handset keeps working past three months without customs IMEI registration.
Registering the IMEI late and being assessed duty on the phone's full value.
Taking a room on 'wifi included' without asking how many rooms share the line.
Paying for Telkomsel's coverage premium for a life spent entirely inside the urban area.
Letting a shop register additional lines under your passport and exhausting your allocation.

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