Google System Design Interview Question

Design a system to hand out telephone numbers for Google voice.

You want to present numbers to people such that:
a person sees 10 numbers at a time
no two people should see the same numbers at the same time
they get 2 minutes to choose one of those numbers or ask for more. If they 
choose one after the 2 minutes are expired, the request fails.


Where you would put the various data elements - in a database, application 
servers, front-ends or the browser. 
What kinds of data structures you would use.