As likely already know, DNS servers translate host names to IP addresses. Typically when the ooma Hub is placed in between the modem and the router, your wireless router should have its DNS server set to the IP address of the ooma Hub (automatically via the DHCP protocol). Next, when your computers connect to your wireless routers, you should see them pick up the DNS server configuration from the router (automatically via the DHCP protocol).
In your case, likely the DNS server is set statically on the computers themselves or on your wireless router. A quick way to check what your DNS server is set to is to use the "nslookup" from the windows command prompt or OS X terminal.App. To test this, type "nslookup" at the prompt and type in the address of "setup.ooma.com" The "Server:" field will tell you what your DNS server is set to. Here's an example successful output:
Code:
myMac ~ 506$ nslookup
> setup.ooma.com
myMac ~ 506$ nslookup
> setup.ooma.com
Server: 172.27.35.1
Address: 172.27.35.1#53
Name: setup.ooma.com