Toll_allow is good to block some or all outbound calls, but we take it a step farther for inactive phones.
We edit the context for inactive extensions that we want to keep registered but otherwise unusable for customer
View attachment 3565
This keeps the phone from dialing ANYTHING by default. For a couple of customers, we create an extra dial plan in the "nouser.customer.domain" context to play a reminder message to contact appropriate people to activate the user.
We've only needed to use the method for a couple of customers that fluctuate staff size enough to turn off billing for users for several months at a time.
In a rare case, we had to do a similar special context for a customer who refused to pay bill for an extended period. In that case, any call would route to a message then option to be connected to billing departmnet.