Hi to Singapore.
There are two network operators in Brunei: DST and Progresif Celular (formerly b-mobile).
DST has better coverage, even LTE, but higher prices.
Progresif has lower coverage, but lower prices too.
The data-only prepaid SIM of DST is called Go!broadband.
More info here:
http://www.dst-group.com/broadband-services/
Data SIM on Progresif is called YES!Zoom and is used to be "real" unlimited:
http://progresifcellular.com.bn/38-2/
They don't have much info on their website.
This guide may be helpful, even prices can be outdated as it refers to b-mobile (their predecessor):
http://bruneitravelguide.com/b-mobile-zoom-broadband/