You should create one emergency outbound route for each location, check the "Emergency" type, enter a proper caller ID in the "Route CID" field and then set up one or more patterns in each route's "Dial Patterns that will use this Route" section in the following way:
a) If all extensions at a location can be represented by a pattern (for example 220-229 => pattern 22X), you should enter 911 in the "match pattern" field and the pattern that matches extensions (e.g. 22X) in the "CallerID" field
b) If extensions at a location cannot be represented by a pattern, in the "Dial Patterns that will use this Route" section add one line per extension with 911 in the "match pattern" field and the extension number in the "CallerID" field
c) You could also use a combination of a) and b) - for example a couple of patterns and a few extension numbers - using either a) or b) is usually cleaner and more maintainable
Finally, select an appropriate trunk for each outbound route, advise VoIP.ms that you'd like to test 911 routing and eventually test.
When someone dials 911 from their extension, the system will select a route based on the digits (911) and the extension number (by matching the CallerID field). In other words, dialing the same digits (911) from different extensions will result in different outbound routes being used for the call based on the originating extension number.
If you need help with defining patterns, just hover over the question mark beside the "Dial Patterns that will use this Route" label and read the hint.