WhatsApp only added support for multiple devices a few months back. Prior to that, your phone needed to be on and connected to the web, even if you were using WhatsApp Web to send messages. That’s no longer required but it’s still not possible to use one account on multiple mobile devices. It looks like this might change.
True WhatsApp multi-device support may be coming soon
The multi-device support that WhatsApp introduced a few months ago was a welcome change. It no longer requires the phone to be connected to the internet. The messages can still be sent using the web client or through WhatsApp Desktop.
What it still doesn’t allow you to do is use the same account on multiple devices. If you want to use WhatsApp on another phone, you must shift the account over and the messages will no longer be delivered to and sent from that device.
WABetaInfo has spotted support for “multi-device 2.0” in the early beta builds of the app. It will let you link another mobile device to the same account. The chat history will be synced when the device is linked the first time. Thereafter, it will be possible to use that same account on multiple linked devices.
It’s too soon to tell if this feature will be restricted to tablets only or if it will be made available for smartphones as well. It would defeat the purpose if the feature was kept limited to tablets.
Even in that case, there are plenty of best Samsung tablets that existing Galaxy smartphone owners could keep using their WhatsApp account on.