Activating a pre-paid SIM depends on the operator from which you received it. If possible we re-commend you activate it online prior to inserting it into the monqi phone. If you need to call an activation number it can easily be done by adding the number as a contact from the parent phone. If you need to read an SMS from the operator you can do so by going to child activities on the monqi parent app.
To see the requirements from various Operators follow the links below.