How to use the same mobile telephone number for different domains

How to use the same mobile telephone number for different domains

We provide email facilities to a number of different domains hosted on our servers (4).

We act as administrators to each of our domains - managing/setting up dns and email addresses etc

Our intention is to replace our email server with Zoho for each of our users (Domains) currently we are trialling with two domains.

How can we setup new users (Domains) using the same mobile phone number?

Thank you

Andrew