what happens if i call 911 using this service?
That depends on the service you set up on the Obi. The Obi does not come with any service for making regular calls, you can call other Obi endpoints using the Obitalk service. You must set up a sip provider (or google voice) as your service provider. If they provide 911 service, the Obi can be configured to place the 911 call correctly.