Well GPS yes it would be too late but the cell location data should have been available for a few days in the subs HLR so they would be able to identify the country the phones were last in. Then you speak to the the local Telco and pull it out of their VLR. Generally you'd have roughly a two day window for this. However I'm sure some billing data was written into a database if the phones were ringing and normally this should include some location data that would be available for a fair while
Obviously if all the phones were turned off in Malaysia then you are up shet creek