If you’re on Direct Routing, blocking calls is as “simple” as ensuring that there is no route to the destination in the Voice Routing Policy assigned to the user placing the call.

For example, if we have a voice usage for national calls that looks like this ^\+(1\d{10})$ then any call that matches +1xxxxxxxxxx (that’s ten x if you’re wondering) will be allowed through. Carrying on with our example from previous posts of blocking calls to the 425 area code, we could change the route pattern to

^(\+1((?!425)|(\d{3}))\d{7})$

And calls to the 425 area code would no longer match this entry. That regex looks a bit gnarly. The +1 will always need to be at the start. (?!425) means “not 425”. The | is an OR, and (\d{3}) is any 3 digits. This says “We need +1 then (Not 425 but any other 3 digits) then 7 more digits.

If you have multiple voice usages – perhaps for service numbers, national, and international – you should be able to modify only the voice route associated with the national usage to block calls to the 425 area code.

This will work because a call to +1425xxxxxxx wouldn’t match with other typical usages, like service numbers (2xx-8xx) or international (country codes other than +1). However, if you have a more complex setup of usages and routes, you will need to ensure that a route further down the ordered list of usages does not allow the call. That is because while usages are evaluated top-to-bottom, evaluation continues until a route match is successful AND the call completes OR until the list is exhausted.

If you have ^(\+1((?!425)|(\d{3})\d{7})$ route in a usage above ^(\+1(\d{10})$ then a call to the 425 area code would be blocked by the first usage but would match the second usage.

This will definitely catch people using (.*) as a catchall for international calls at the bottom of their usage list. This also means that you cannot simply create a usage and route that blocks a call and insert it into the list of usages above a rule that would allow it. Your exception/block must take place in the same route regex that would match and permit the call.