D'apres Jono <nothanks@blueyonder.invalid>,
[color=blue]
> you may find the Linksys/Sipura help files on this page a worthwhile
> read.
> <http://www.provu.co.uk/support.html>[/color]

Many thanks. I found interesting info in
[url]http://www.provu.co.uk/pdf/sipura/spa_backtoback_2x_spa3000.pdf[/url]

At present, it works both ways (PSTN <-> VOIP) using an intermediaite
registrar (I am using 3CX for test purposes). A drawback is that the
PSTN-to-VOIP CID is blocked (replaced by the incoming extension number
of 3CX)

I will not be using two SPA-3000 (unless there is no other way and I
change my plans) but a ordinary SIP phone on the remote end (at present
I use a softphone for tests). So I still have some work to do...