Just to share my experience on data roaming using TPG (Simba) and Giga.
I did not subscribe to wifi onboard as the plan have free data roaming to Malaysia and for departure Sunday cruise the ship is docked at the 2 ports for quite long. I stayed on the ship.
TPG which use Celcom is surprisingly not bad. Signal at Port Dickson is not so stable. Very faint signal when stand at the balcony. No signal in the room. But there is signal at Lvl 19 Palm Court which is quite usable. Could surf the net, answer emails and send WhatsApp. Signal at Penang was very good. Could receive the signal while lying on the bed, no need to go to balcony or Lvl 19. The ship left Penang at about 4.55pm and sitting at the balcony, I could still surf at manageable speed till 6.20pm.
Giga has no signal at both ports.
Edit : Giga might not have worked because no free roaming.