Adding dynamic phone numbers to pages

So it would be:

Visitor A, show phone number: 111-111-11111

Visitor B, show phone number: 222-222-2222

Visitor C, show phone number: 333-333-3333

Correct?

If so, I mean what is the rule that shows the phone number to Visitor A and a different phone number to Visitor B. Would it be based on whether they have a cookie or something else?