Only contact BT if they supply your broadband, as the issue is just affecting broadband it is contact your ISP, and explain the steps you've already gone through

> Only contact BT if they supply your broadband

Duly noted. I wasn't entirely sure if this was 'broadband' or 'line'. Further rummaging on the net seems to show a number of people on ADSL2+ with the same lost-sync problem.

The probability of the line losing sync heads rapidly towards 1 as the number of rings increases - anything over 4 is pretty much guaranteed to kill the line.
So I have set the fax to pick up after just *one* ring (two was always good to filter out accidental calls), and whilst this isn't perfect, it seems to have significantly reduced the number of line drops.

On the upside, I do now have a handy stats collection script (RouterStats isn't very OpenBSD compatible) that gives me a on-liner timestamped output (with all the relevant numbers) - easier to follow on-screen and spot when something happens.

If the helpdesk comes back with anything useful tomorrow I'll be sure to add it here. Likewise if I hit upon a miraculous fix or even one that makes the problem 'acceptably minimal'.