I have more zeros than you... is the name of the game. Few days ago, less than a week in fact, XL announced they have 0.00000...1 tariff (six zeros). Now Indosat came with 11 zeros. So it seems that your call is free after 90 seconds. Again this applies not just for on-net but also for off-net calls. (Wondering whether they make money at all...)
Indosat website is down (from my LAN) at this moment so no further details :-)