Did you try this? (From the website linked by Dan in the comments to the main article)
Getting Emergency Calling (i.e.: e911) to work (optional)
Fewer do each passing day, but if you still have a regular old POTS line at home (or even an analog telephone adaptor connected to a VoIP service provider that offers E911 such as VoicePulse, Vonage, and cable services such as CableVision, Comcast and Time Warner), and you connect the service to the “Line” port on the OBi, you won’t have to do anything to get emergency calling service. By default, the OBi will send any “911″ call through whatever is connected on its “Line” port. (Note: In many regions within the United States, even a disconnected POTS line may work with 911 calling services — but please check with your local carrier to make sure).
If you don’t have E911 coming into your home, there are several VoIP services available that offer low-cost emergency services calling. One such service is offered by popular pay-as-you-go VoIP provider CallCentric for $1.50 per month (there is also a one-time e911 setup fee). If you sign up for the company’s Pay-Per-Call plan, and fill your account with a minimum of $5, you can add the 911 service and the fee will be deducted from your deposit.
There is a small catch: Unless you have a spare VoIP adaptor to install the Callcentric (or other provider’s) service on (in which case you should simply connect the “Phone” port on the external ATA to the “Line” port on the OBi using a basic telephone cable), you will have to dedicate one of the Service Provider ports (SP1, or most likely, SP2) solely to 911.
To configure it, add the service provider to SP2 using any of the methods illustrated above (OBiTalk, which comes with pre-configuration for 8 service providers, including Callcentric, is the easiest method).
To ensure that 911 calls over the OBi are routed correctly, connect to the device via the built-in configuration tool (point your browser to the OBi’s local IP address) and make a small change to the long dial string setting located at Physical Interfaces/Phone Port/OutboundCallRoute. The default setting is:
{(< #:>|911):li},{**0:aa},{***:aa2},{(Mpli):pli},{(< **1:>(Msp1)):sp1},{(< **2:>(Msp2)):sp2},{(< **8:>(Mli)):li},{(< **9:>(Mpp)):pp}
Uncheck the “Default” box on the right, and make the following small change to the long string: Change the first instance of “li” to “sp2″. The result will be this string:
{(< #:>|911):sp2},{**0:aa},{***:aa2},{(Mpli):pli},{(< **1:>(Msp1)):sp1},{(< **2:>(Msp2)):sp2},{(< **8:>(Mli)):li},{(< **9:>(Mpp)):pp}
Click “Submit” and “Reboot” the device.
Ideally, we could easily test 911 calling. Unfortunately, ensuring that 911 calling works on your OBi is a bit problematic. Calling 911 as a test is highly frowned upon by emergency service operators, and is even illegal in some states. The only surefire way to test 911 is to call your local law enforcement agency’s non-emergency number, hope to get someone on the phone that understands what you are trying to accomplish, and schedule a 911 call. It’s a bit of a hassle, but definitely encouraged.
When you’re done, you’ll have a complete phone system, with it’s own phone number(s), free phone calls throughout the US and Canada, voice mail, call forwarding and dozens of other “premium” services, for pennies. And you’ll help speed along the landline’s obsolescence. Good riddance.