When someone calls you, the voice of the kit reads the caller’s phone number or reads the caller’s name saved in the contacts ?

The kit reads the number correctly. Unfortunately it does not have access to the name of the contact. To see the name you can for example place the phone on a stand in order to be able to read the name. You can on some phones personalize the ringtone of the phone for a contact, this can allow you to recognize who is calling.