The easiest way to communicate is via the internet, and wifi is readily available all over the island. The connection is usually SUPER slow, and it is rare that you will get a very good one, but it is still available. Email and facebook are good ways to keep family and friends updated without spending a bunch of money. If you want to call someone internationally, the cheapest way is skype. You can download skype on any computer or as an iphone application for free. You simply buy credit and then call the person from the program, and voila! Just know that skype uses a lot of bandwidth and requires a pretty good signal for the connection to work clearly. It will also slow down the internet for whoever else is on that connection with you. I was in Bali for over two months and only used $7 in credit, and that’s probably for over 150 minutes. If you aren’t bringing a computer, there are internet cafes as well, and they are easy to find.
There are no pay phones in Bali that will allow you to use calling cards. You may be able to ask the person you are staying with if you can use their local land line, but im not exactly sure how that works and they may ask you for money to do so.
If you want to have a phone for local calls within Bali, you can bring your cell phone (or an old phone) and buy a Balinese SIM card to put inside. Just go to any cell store, buy a SIM card, have them activate it (just let them do it, its easier), and buy credit, and you will have a local number and can make calls for very cheap. A SIM card is only about $4 and the credit is cheap as well, so this is the easiest way to keep in touch with people who are on the island. Don’t even bother using your actual phone on an American plan, it will be ridiculously expensive and not even worth the effort. If you don’t buy a Bali SIM card, you can keep your phone on you for emergencies if need be.