if you use in iPhone/iPad, isn't there option to convert online?
i forgot how; did so few months back to my faraway postpaid supplementary.

both celcom and digi not yet become one. in-progress.

if you visit ex-Celcom store to sign up CelcomDigi postpaid plan, your SIM will latch onto Celcom network, app is Celcom Life, and CS call centre handled under Celcom.

if you visit ex-Digi store to sign up CelcomDigi postpaid plan, your SIM will latch onto Digi network, app is MyDigi, and CS call centre handled under Digi.

iinm, CelcomDigi will have to surrender some network bands back to gomen.

i only read. didn't keep track.
not sure if they already surrendered or "that'is-why-they-are-still-redo-towers-to-get-off-those-bands" not yet surrender.

iinm, they are allowed to remain as 2 brands for time being, but eventually have to become single brand. They are not yet fully integrated, can see they are still working on tuning towers, which i believe is about freeing band that they have yet to surrender back to Gomen. Even SIM latches on to which brand you signed up through.