To do either of the following you have to establish a static IP address, obtained from your router, for your Ooma device. In most routers you can assign a static IP address for a device. Or in Ooma Setup you can assign a static IP address obtained from your router. If you need more detailed instructions I can post or you can seach this forum to locate them. Also If you go into Ooma setup, under "Network" than "MODEM Port MAC Address" select "Use built in", than select "Update".
First: With your Ooma device Placed placed behind (LAN side of) your router, place your Ooma device in the router's DMZ.
Second: With your Ooma device placed behind (LAN side of) your router, create a rule(s) to open the following ports in your router.
Ooma uses the following application ports for data and voice traffic:
UDP 53, UDP 123, UDP 514, UDP 1194,UDP 3386, UDP 3480, UDP 10000-20000, TCP 53 and TCP 443.