Thank you Martin and DracoFelis for that info. I'll try those ideas on the weekend.
However, it is confusing for me, that with my PSTN number mapped to
050xxxxxxxx@xxx.xxx.xxx.xxx, e164.org can call me via ENUM (test), OzTell can can call me via ENUM (WebDialer), but Sip Broker can't seem to call me via ENUM.
The ATA I'm using is the "ADSL Modem SV III", provided by NTT-West. This appears to be the standard ADSL modem they supply for their "Flets ADSL" service. It has a built-in SIP-compliant ATA (supports G.711 u-law codec only).
http://www.ntt-west.co.jp/kiki/consu...sv3/index.html
(in Japanese)
http://asahi-net.jp/en/support/guide/ip-f-sv.html
(an abridged guide in English)
The ATA is not locked - you can set it to use any SIP provider - however it is designed specifically for the bundled / packaged "IP Phone" service provided by Japanese ISPs using NTT's "ADSL Flets" connection. The dial plan is hard coded, and calls are dialed out in Japanese-domestic format.
The most flexible solution for me, would be to run Asterisk on an internal computer, have the ATA register with my Asterisk server, and then get the Asterisk server to take care of everything. However, I'm trying to see if there is a solution that would require no additional hardware, so that many other subscribers in my situation can take advantage of ENUM and VoIP peering.
edited: spelling correction