You are right that LTA is keeping mum on the opening schedule.
The original schedule is to open the stages in sequence, starting
from Stage 1 in 2007 to Stage 5 in 2010. However due to the Nicoll
Highway incident, LTA has not make any concrete announcement on the
revised schedule.
However, we may infer how the it will open based on proxy source. A
close proxy is Circle Line Art
Competition, where LTA invites artwork/design to be
incorporated into the new Circle Line system. The competition has
two phases: first phase for stations in Stage 1-3, and second phase
for Stage 4-5. Hence, we can infer that it is most likely that
Circle Line will be opened to public in two phase: Stage 1-3 then
Stage 4-5.
