Cycle was thinking very hard :
Can the telephone drop wire (the wire that comes into my house from outside)
be temporarily disconnected, without causing anything undesirable to happen
to the telephone system?

Officially you are not permitted to touch it. Unofficially they will
not notice if you disconnect it briefly and reconnect it. The exchange
runs a line test during the wee hours, which is designed to ensure
there are no problems/faults/disconnections on your line.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org