Multipe emails under one domain

I have a business account I pay for and want to add a personal account (for free?). I can't set it up as they both have the same phone number and I have read the limitations on that. Can I add one more email under my current domain for no additional charge (in effect free?). Or can I add a personal address xxxx@zoho.com under a domain name xxxx@domain.com? Or does it have to have the matching domain part? Thank you.