Shipping confirmations are sent via whatsapp via Tokopedia, Shopee and Lazada.
Logging in / MFA is done via Whatsapp.
You can have a whatsapp for business (which is a separate app from whatsapp but same thing but has built in ecomm tools)
Grab/Gojek/Angas drivers won't text you, but would whatsapp you (cause it's free.) there is a built in dialer/voip into Grab/Gojek, but it sucks and sucks so much it can be useless unless you are ina n 4G LTE locaton and even then - it sucks. I've had countless drivers message me from a grab/gojek hail to confirm location, send live location, etc.
Whatsapp is the status quo for communicating with friends, dates, co-workers, contractors, etc. No one wants to pay for an SMS plan - in Philippines it's barely there but most people have moved on due to tons of fraud/abuse/load scams (load is the credit for Globe/smart, it's called pulsa in indonesia) so many people just all together turn it off.
OTP/MFA from all the major indonesian/malyasian and PH banks do Whatsapp MFA. BPI, BDO, Mandiri, Permata, BCA, Mayabank, HSBC, etc. Yes, even HSBC.
It's even a big thing with USA banks - https://www.telemessage.com/citi-goldman-sachs-hsbc-and-othe... but that's more for collusion then just ecommerce and general daily life activity.
So tl;dr Whatsapp is required in SEA for daily life, otherwise you're the outdated outlier that needs to do phonecalls.