The Indonesian mobile phone market is heavily competed and prices are low; you can pick up a prepaid SIM card for less than Rp 20,000 (2,5 or 3 U$) and calls may cost as little as Rp 1,000 a minute or less (subject to the usual host of restrictions). Indonesia is also the world's largest market for used phones and basic models start from Rp 250,000.
The largest operators are Telkomsel (brand Halo, simPATI, AS), Indosat (brands Matrix, Mentari, IM3) and Excelcomindo (brands Jempol, Bebas). Shops which sell the sim cards are prolific.
If you have Global System Mobile (GSM) cellular phone, ask your local GSM operator about "roaming agreement/facility" in Indonesia. Most GSM operators in Indonesia have roaming agreement with various GSM operators worldwide. Using roaming facility, you can use your own cellular phone and GSM SIM card in Indonesia.
Most Indonesian operators use GSM, but beware of the few offering CDMA phones: they are slightly cheaper, but generally not usable outside major cities. Be sure to double-check when buying!
