I meant my home TM wifi.
As i said earlier, i normally manually top-up the FOC 1GB.
The FOC 1GB can be purchased anytime
If i type 'Broadband vol' & send to 22188, Celcom will reply with this:-
Additional volume: 100MB@RM3, 500MB@RM10, 1GB@FOC, 5GB@RM50. To get additional volume, send ON VOL100MB/ ON VOL500MB/ ON VOL1GB/ ON VOL5GB to 22188.
That ~2GB balance was the current balance after usage at that point of time after I SMS 'vol status'

Sorry for any confusion bro

It will be charge to your current bill & can be seen in your itemized bill later on. But since it's FOC, should not be a prob