Is it possible to use a twin SIM with the MP01 so I can use it on the same number as my smartphone?Updated 2 months ago

It depends on your operator. Some carriers offer a second SIM (at a monthly fee) others don’t. Every country has different operators each with their own policies, please check with the operators in your territory.
It is possible to turn on call forward and take calls on the same number as your smartphone, even when it is switched off.
In addition, as the phone will be sold SIM-lock free, when you are travelling abroad, the MP01 will work with a local SIM in any country (Japan and Korean excluded as do not have GSM).