BT 1020 - Manual (Page 18)

If you also have a videophone or BT Soft Phone associated
with your BT Broadband Talk number you can also use them to
make simultaneous calls up to a total of 4 calls across all your
BT Broadband Talk phones.
In situations where there are already 2 calls in progress on
BT Hub phone handsets, a warning:
LINE IN USE
is displayed
on any other additional BT Hub phone handsets you may
have around the house informing you that you cannot make
any more calls. There is also a special busy tone presented if
you press the
button to make a call when it is not
possible.
When using multiple handsets you can make internal calls
between handsets or transfer a call between handsets. You
can only use this functionality if there isn't call in progress on
another handset.
Making calls with BT Broadband Talk
18
Hub Phone 1020 – Issue 3 – Edition 1 – 05.10.07.07 – 8423 H
8423 Hub Phone 1020 Iss.3 [1] 12/10/07 12:25 Page 18