Telephones and mobile phones
Telkom is the suppliers for land lines, but not very many private homes ever bothered as it was expensive and unreliable in the past, and mobile phones are far better, easier and cheaper now.
Getting a land line can be seriously hard work, and pointless for most people.
Mobile phones are a different story.
There are mobile phone shops everywhere, literally hundreds in every town, commonly with several on every larger street.
Shopping centres commonly have 10 or more shops, all selling contract free, unlocked phones.
Some suppliers sell locked contract phones, but I'm less than sure I'd ever bother with one.
There are many SIM card/airtime suppliers in Indonesia.
Telkomsel have a very wide coverage, working everywhere I've ever been, but I scrapped them because of the massive level of spam SMS messages they sent.
It got sick of it, so I got rid of them.
XL and Indosat are probably next on the list for coverage, but they also send a load of spam (as of last time I used them), and one company ripped me off with scam, charged SMS messages they claimed I'd signed up for.
As luck would have it, they did it to a government minister at the same time, so got dragged over the coals.
They refunded my money.
Many operators were implicated in this theft.
On Lukereg's advice, I tried the 3 network's 'always on' deal.
You pay Rp50,000 per year for the card, then add credit and internet quota as you require.
Unlike most operators, the credit and quota have no time limit, lasting until the card expires (if not renewed), or until used up.
The signal is a bit on and off in the countryside, but works well in the cities. Their internet service varies in speed, but I can usually use skype without serious problems.
All operators have an internet service, and all are getting better and faster since the Bolt network opened up in this country. Their service is very fast, but can be expensive if you're into streaming. For general surfing, emails, and basic stuff, Rp29,000/month gets you 1 gb of data, all delivered at fast speeds.
As with other networks, they have a range of WiFi units, ranging from the small and portable to the in house mains powered devices. I use a Bolt fro when I'm out with a laptop, and I'm very pleased with it.
However, the service area is limited, so check before you buy.
Indonesia has "Internet sehat" (healthy internet), so a lot of porn sites are blocked.
Sadly, some political sites get hammered as well, so it can limit the users ability to search for political titbits,if that's your interest. That's not to suggest Indonesia has general political censorship, these sites might very well have porn or extreme violence as well.