How to Limit Inbound and Outbound Calls with One Trunk


I have a system set up with 10 extensions for one office, and 5 phones are another office, but located in the same building. The PBX itself is in a datacenter - not local to the office building. The 10 extensions are one business who are using 3 lines/call paths. The 5 extensions are another business with 2 lines/call paths.

We use one carrier with one trunk setting for inbound and outbound. I know I can set the max channels limitation in the SIP trunk config, but we want to actually limit it per the extensions in the system… so my thinking was to do something like this:

  1. Keep the plain SIP trunk as is, without limits. Then
  2. At our provider, configure the dialing rules for the 5 extension customer to prefix inbound calls with 1234, for example. Then
  3. Create a custom trunk to remove the 1234 prefix from inbound calls and pass those calls on via Local/$OUTNUM$@from-trunk-sip-CustomerA
  4. Create an inbound route for _1234XXXXXXXXXX and pass that route along to the custom trunk configured in 3 above
  5. Create a new SIP trunk called CustomerA where the channel limit is 3 (or should that be 6 for inbound and outbound channels?)

I tested this on a sandbox server and the calls come in and pass through the stuff fine… except calls aren’t being limited. I can still call this system from my cell, from a fax line and from another cell when I had the limit set to two max channels (calls?)

Is there a better way to do this, or am I doing it completely wrong in the first place? How can I actually divide these businesses into their separate limited call paths. We have to limit it as we haven’t been restrictive before, yet the customer only wanted to pay for 3 call paths from the beginning.

Thanks for all your help everybody! If you need more info, please let me know.