I have searched for others with a similar problem but found no matches. The problem is that both incoming and outgoing calls are cut off by the engaged tone. This is an intermittent problem and some calls are not affected at all. The fault has been reported and the line tested with no fault found. The phone system includes extensions, BT Router. (version 3). Service is phone, BT vision and BT Internet.
The current situation is that I have disconnected the extensions at the master socket and have only the BT router and a phone connected via a microfilter to see if this cures the problem. However, with the problem being intermittent, I will not know if this is a cure (pointing to a wiring or equipment fault at my end) unless we make or get a call that is cut off. The self help guide from BT is fine for a permenant fault but is of limited use for an intermittent fault.
What I would really like to know, preferably from someone who has a definitive answer based on technical knowledge, is: could an equipment or wiring problem on my side of the master socket interupt an established call and cause an engaged tone, or is this likely to be a network/exchange fault?
With only router and phone in test socket, and with a different ADSL filter plugged in, probelm still there. Have reconnected the extension wiring and disconnected the phone from the master socket. If the problem recures now then it must be either the router or the line.
Just in case it helps someone else, BT rang this afternoon to say that they "had made some adjustments at the exchanged" and the problem should now be fixed. So, not the phone and not the router.
Not being an expert, I can't be sure, but I suspect that a problem as described during incoming and outgoing calls, has to be a faullt between the two phones and not at either end. If that is the case, it would have been helpful if the person on the helpdesk new that rather than talk me throught a seriies of actions that were at best inconclusive for an intermittent fault.