Unique customer relation number

Unique customer relation number

We are setting up Zoho Enterprise and we have the following problem.

Why isn't there a unique ID for each contact that can be seen from the contacts details screen?

For instance a customer calls and the agent asks, hello may i have your customer relation number?
I'm used to this being quite normal in CRM systems. If you have 10 customers with the same last name how do you quickly find the correct record?

The data from the old CRM system has these unique customer relation numbers which i can import to a custom field of course. But then there won't be autonumbering of new customers anymore once we start working with Zoho.

So my questions is why isn't there a unique ID and does anyone know of a work-around for this problem?

Perhaps it would be possible to display the contact ID somehow and use this?