If you want cheap, use calling cards. Based on my husband's research, Phoenix calling card is the cheapest to call Indonesia. If you are not sure, just go to the shop selling the cards & they'll be able to tell you the prices.
My maid does not chat for long, so I see no need to 'save' this type of money cos the card has expiry date & if you dont't use up the remaining value, it'll expire also. I think the expiry is within 1 month (can't rmb). My maid hardly calls back, how to finish using $10 worth of calls in a month?
I let my maid call back using IDD 018 (Starhub home phone). She chats for around 10min, I remember the bill was $2+ for that phone call. She calls back probably once every 2 months?