Except for digi, maxis & celcom will charge u if u exceed the limit/threshold..
so u better watch out the utilization of the data each time..

moreover, the limit is include download/upload..

For digi, they will throttle your speed from 700 kbps to 128 kbps w/out charging any of the cents if u exceeds..

for often roaming data usage, better check your internet roaming settings under settings --> network..

off it so that u cant use your data if u roaming..

thank you