After upgrading to firmware 3.8.1.9 I have found it impossible to call in or out via a PSTN trunk. Incoming calls are eventually dropped although the PBX call log shows them as having been sent to voicemail. Outgoing calls immediately play the busy tone (engaged for fellow UKers.) I have tried upgrading to both the .all and .rst files then restoring my settings. It matters not which way I do the upgrade. I used the Draytek email support form to report this last night but I'm not sure if it went through as the browser page didn't give any acknowledgement after hitting send. I guess I'll find out eventually. In the meantime, I've downgraded the firmware to 3.8.1.8 and everything is fine (apart from the terrible audio quality which has been an issue since day one.) Has anyone else had any similar problem and did you find a solution?

Well the support email did get through. If I get a resolution through that process I'll post the results here for the benefit of anyone experiencing the same sort of problem.

I had an issue with non of the services working, such as voicemail, I didn't test the PSTN.
Anyway here is a link to the Beta Firmware Version Draytek sent me which solved my issue, its's worth giving it a go. https://www.dropbox.com/s/0cu6lf0inutzyk3/vbx2k_3883_RC1_VT3.all?dl=0

Have you tried to change the codec for the call quality issue?
IP PBX >> PBX System >> Phone Setting

I found this to help.

I have messed around quite a lot with codecs & mic/speaker gain. I have it in a usable state although the audio quality really does leave a lot to be desired.

The security advisory which accompanied the release of 3.8.1.9 leads me to believe that my configuration is not at great risk from the associated vulnerability so, unless events prove me wrong, I'll stick with 3.8.1.8 until a release from Draytek supercedes 3.8.1.9. Thanks for offering the beta though.

3.8.8.4 allows outgoing calls but incoming calls are not forwarded to an extension. Anyone else having this problem?