The free number included with your account cannot be changed while the account is in Trial status.
Once you upgrade to a Paid plan, you can remove the included number and add a different one — either by purchasing a new number or bringing your own (US/CA) VoIP or landline number.: Add a Number.
Sakari accounts will continue to include one free active number at no charge, as long as that number is based in the United States (+1), Canada (+1), or the United Kingdom (+44).