Phone networks

There are four phone networks in Indonesia: Telkomsel, XL, Indosat (IM3), and Smartfren.

Telkomsel has the best coverage, including Bukit Lawang, but they are government-owned and it is not always easy to buy a SIM card. XL and Indosat may both have coverage in Bukit Lawang, but Smartfren does not.

IMEI blocking

All foreign phones are blocked for use in Indonesia, except when using special tourist sims (including esims). Telkomsel sell a tourist Esim, but this requires you to go in person to their GraPARI store, where you could just as easily buy a physical SIM. The GraPARI store at Medan airport closed down, and the queues at GraPARI can be long, so this is very incovenient. Therefore, the XL tourist esim above can be more suitable, providing your phone supports it.

If you want to unlock your phone for use with Indonesian non-tourist SIM cards you can do so only before leaving customs upon arrival in Indonesia. There is a $500 customs limit (which covers all goods that will remain in Indonesia, as well as your unlocked phone), above which you'll pay around 35% tax (on the excess). Phones are valued at current market value, not the original selling price. Unlocking your phone can be a good idea if your phone doesn't support esims, or if you are planning to stay in Indonesia along time.

SIM registration

Indonesia requires locally sold SIM cards to be registered using ID. For Indonesians this can be done using their ID and family card numbers via online. For foreigners, a passport is required. Foreigner SIM card registration will typically not be possible at most retailers.

XL sell a tourist esim that can be purchased and registered fully online, using your passport. You might have trouble with payment, which is via credit card. However, if your phone supports esim, this is a convenient option.

Non-Indonesian Esims

Non-Indonesian Esims offer internet access for phones that support esim (e.g., Iphone, Google Pixel) without ever buying a SIM card in Indonesia. When choosing an Esim it's best to find one that uses Telkomsel. Costs per GB will be higher than the cheapest local SIM, but it is more convenient: however, note that you won't get a local phone number.

Wifi

Wifi is available in many places in Bukit Lawang, using fibre optic internet. Speeds are typically 10-20mbit shared among a whole restaurant or guesthouse. Powercuts are fairly common, and will tend to mean no wifi. Having phone internet is a good idea if you rely on internet access.

WhatsApp

WhatsApp is close to ubiquitous in Indonesia. Providing you have internet access, it will be possible to make calls and chat with Indonesians if you install WhatsApp.