1. Map a DID to a *non*-PBXes account at e.g. e164.org
2. Call via SIPBroker ENUM (e.g. **275*013... from FWD) - Call succeeds
3. Call via OpenSER ENUM - Call succeeds
4. Change the mapping to a PBXes account
5. Call via SIPBroker ENUM - Call fails
6. Call via OpenSER ENUM - Call fails
If you change it back, calls succeed again.
Apparently, PBXes is giving a 404 to the INVITE, even though the address in the SIP Request-Line is correct, and can be reached directly by a SIP phone.
If anyone at PBXes is interested in the Wireshark captures of the OpenSER sessions, please email me. This might be applicable to a lot of other ENUM-enabled switches trying to connect to PBXes accounts.