WhatsApp multi-device 2.0 will allow people to connect an additional mobile phone or tablet (WhatsApp for iPad / Android tablet) to the same WhatsApp account in the future, writes WABetaInfo on its Twitter page. If true, this will help people to use WhatsApp with an additional phone or pad without using a key number. This will break the cycle of having multiple SIM cards for different WhatsApp login.
This is a future update that may or may not come. The final update may be completely different from what is predicted here. The Meta-instant messaging app constantly updates itself with in-app features to make it easier to chat with other processes in between.
In the meantime, you can use WhatsApp on one phone or one tab or you can connect a web device to it. An additional mobile phone or pad that connects both iOS and Android will save time and effort for WhatsApp users. Every time you change the phone and install WhatsApp you are generated a six-digit code that is only sent via a registered mobile number to synchronize data and chat history. This may not be required with the multi-device 2.0 update.