We reported a few weeks ago that WhatsApp was working on a way to let you use the same account on multiple devices.
Currently, your account is tied to your physical device and phone number, rather than something more portable like a user name and password, meaning you could really only use the app on one device at a time.
WABetaInfo has discovered that this was about to change, with Facebook building in a new UI which allows users to link multiple devices (up to 4) and use them at the same time.
Today WABetaInfo reports that Facebook is also working on a way to sync your message history from one device to another.
The feature would require your device be connected to WIFI, due to the volume of data which will need to be transferred. It appears the data will remain encrypted in transfer.
After the data is transferred linked devices should remain in sync, as all future messages will be delivered to all devices.
The feature is still under development, and it is not known when Facebook will be rolling it out.
Read more at WABetaInfo here.