It will magnetically connect to the side of the tablet. It will charge like this too.
Phone will be small like the current iPod nano size. Big enough screen to use comfortable when away from tablet to make calls and use camera.
The phone also has all the important modules like camera, sim, gps etc.
When you are going out just snap the phone off and go. It has the modules so you can have all the necessary tools when you are away from home.
When its connected to the tablet it uses the connection to charge and also allows tablet to use the sim and camera modules if needed.
Also tablet can use the phone screen to show notifications. If you want to bigger look at them you can swipe them on to tablet to open the app, or dismiss them from the phone itself.
The place where the phone and tablet connect will have edge to edge screen to make it feel like one screen.
When the tablet is turned on you could use the phone screen to show additions stuff like twitter feeds or something else.
All the technology is available right now, hope some one comes up with the combo soon.