[SR-Users] Users in different domains and multiple domains

Hello everyone! I'm wondering something about Kamailio. Here is the idea: Such and example, I want to give base system which depends on Kamailio to 3 companies in 1 server. So I have 1 Kamailio Server and 4 or 5 Freeswitch server. Thus, I have to set a domain for each company, so total is I need 3 domains. For example a, b, c are users. But they should in the different domains for know which is which. In a word, it should seems like this: a(a)subdomain.domain.com b(a)subdomain.domain.com c(a)subdomain.domain.com a(a)subdomain2.domain.com b(a)subdomain2.domain.com c(a)subdomain2.domain.com or a(a)subdomain.domain2.com b(a)subdomain.domain2.com c(a)subdomain.domain2.com etc... So where can I do this? Remember, Kamailio should in the 1 server and all of domains and users should in this server (I will use Postgres) For more details, you can write. Thank you. Regards.