[humba3]

It is possible after all. For those unaware of the term, a trunk seizure prefix is a sequence you dial to select a certain trunk.. in case of the SPA9000 that corresponds to dialling a prefix to select which of the 4 lines on the SPA9000 you use to call an outside line.

First you need to adapt the phone DP to include the prefix. I chose #x as my trunk seizure prefix (actually, it ought to be #[1-4] since we only have 4 lines. #1 selects line 1, #2 selects line2, etc.

So the phone DP becomes a new element: #[1-4],xxx. (#x gets the secondary dialtone, and then at least 3 digits need to be dialled for the call to be routed). Naturally, this can be extended with all other elements you need to call outside but I decided to keep this one simple since it's a feature I mostly need for testing purposes.

The second part is the call routing rule.

Add an element
<:L1>#1xxx.
and duplicate this for each of the 4 lines. This element ensures that when dialling #1 and then 3 digits, the call gets routed to line 1 and only line 1.

Finally, line 1 gets a new DP element as well to strip away the trunk seizure prefix again:

<#1:>xxx.

This strips away #1 and sends the remaining 3+ digits to the SIP provider.


The only question remaining is why the following call routing element triggers a 503 response to the invite by the phone:
<:L1><#1:>xxx.

This ought to immediately strip away the #1 again, leaving just the digits to be sent to the outside world.. it ought to cut down the work as you don't have to adapt the lineX DPs. But, while I see the SPA9000 find the rule and applying it (the #1 is properly stripped away), I always get a 503 service unavailable response, whereas when I do the stripping in the LineX DP, it works like a charm.