In Indonesia you will found 4 main mobile operators (“Telkomsel”, “XL”, “Indosat”, “Smart”) with different prepaid cards – for example “Loop”, “IM3” and etc. One of them is more expensive but covers mostly all Indonesia area and you will be reachable while hiking in some volcano or camping somewhere further from civilization. Others will be cheaper but sometimes with delay SMS delivery and etc. Most probably the local people are using the cheapest one and has good connection in their exact area.
I recommend for backpacker using “Telkomsel” operator. It has wide area coverage in Indonesia, better than others. You can sms, call or internet browsing, but the signal depend on location, if it’s far away from transmitter tower, you can not doing internet, just call and sms only.
After you choose mobile operator, sometime you will need to put money to prepaid cards (“pulsa”) each time when you will finish your limits. The “pulsa” amount depends on how much you want to put to prepaid cards. Usually its fixed amount – Rp. 5 000, 10 000, 15 000, 25 000, 50 000 or 100 000 Not in all places you can put bigger amount like 50 000 or 100 000 Rp. As well the “pulsa” validation depends on mobile operator – one suggest validation of 1 month, others – to use till you will finish it (no matter if it will be even couple of months).
*) Today (12/30/2016) i browse ebay.com using Telkomsel internet data, i found pop up ads for a few seconds. Oh, i hate that. World already full of advertisement. I heard it won’t happened if you live in Europe or USA. In here the consumer seems no rights to avoid ads.
**) Seems today they already remove the pop up advertisement.
***) Today the ads come through SMS. You will accept some SMS as advertisement when you open it. Could be from Restaurant, ‘Donut’, ‘Pizza’ or ‘Cinema’. Much of travelers not love this things. At least you won’t surprised if it happened to you.
****) The telecommunication ministry release a new policy on 2018 for SIM card. It must be registered by the buyer, not the SIM card seller. I recommend you buy a Telkomsel SIM card at official shop and then you register it on the official shop. Don’t forget to bring your Passport. Here i provide the maps of Telkomsel SIM card official shops:
*) If your hotel around Malioboro area or Sosrowijayan area or Prawirotaman area better you choose the Telkomsel official shops on the 2nd map above. It’s relative closer from your hotel.
**) On December 2018, if you browsing use a Telkomsel SIM Card, you will see a pop up advertisement. This is another way how they make a money. It’s really annoying.
***) There is no good telecommunication operator in Indonesia. The option are bad and worse! I recommend you to use this operator because they have a lot of BTS (Base Transceiver Station). It means they have wide coverage area in Indonesia (good signal). But, it doesn’t mean their services satisfying (high speed internet).