I haven't checked with the telco (Maxis) but is it possible if one (1) SIM card is shared with 2 phones? Meaning 2 phones with the same number can be used to access Whatsapp and make calls simultaneously. If not, can there be 2 SIM cards with the same number, 1 being duplicate?

Cannot.

Whatsapp on 2 devices is easy, they updated it with this feature, you have 1 phone be the main phone, then login on the 2nd phone as a 2nd phone, and both can access

but the main phone is still the "master" one, if you in the future need to change phones/backup/etc

https://blog.whatsapp.com/one-whatsapp-acco...multiple-phones

as for calling, not possible

Thanks for the response. I tried using Whatsapp on both phones last month and although it briefly worked, it's troublesome as I need to log off from Whatsapp on the main phone (with the SIM card) before logging into Whatsapp on the other phone (without the SIM card).

Also, the phone without SIM card will need to be connected to Wifi or hotspot, so it will be useless if there is no wifi or hotspot.

Unfortunately there is no flexibility to have 2 SIM cards with the same number to be used on 2 separate phones. Otherwise it would resolve everything.

i have been using 1 whatsapp on 2 phone 1 year ago, no problem
but when i log out on second phone, it delete all media on my second phone

if they allow that, that is breach of security already LOL like you say can have 2 same ip address in the network, sure ip conflict la

only in spy movie and tv series

go to near target, wait a few second remote hacker doing magic and tada done clone the phone number

Can i hp and 1 LTE watch. When they r not connected via bluetooth, The LTE watch can receive phonecall by the dign/ maxis operator and WA message or voicemessage. But somehow cannot receive WA call.