The ETravelSim Vietnam eSIM works on most Ha Long Bay cruise routes near the bay's main visitor zones and across the Mekong Delta provinces including Can Tho, My Tho, and Ben Tre. Cruise boats further out from the bay's mainland tower coverage may lose signal — this happens on every Vietnamese carrier and isn't specific to one network. Mekong river towns have solid coverage; remote backwater channels and small islands may drop to 3G or zero. Save itineraries offline for boat days.