Digium Asterisk Appliance 50 AA50 Administrator's Manual page 124

Appendix C: Asterisk Appliance 50 (AA50) License Agreement
You may charge a fee for the physical act of transferring a copy, and you
may at your option offer warranty protection in exchange for a fee.
2. You may modify your copy or copies of the Program or any portion of
it, thus forming a work based on the Program, and copy and distribute
such modifications or work under the terms of Section 1 above, provided
that you also meet all of these conditions:
a) You must cause the modified files to carry prominent notices stating
that you changed the files and the date of any change.
b) You must cause any work that you distribute or publish, that in whole
or in part contains or is derived from the Program or any part thereof, to
be licensed as a whole at no charge to all third parties under the terms of
this License.
c) If the modified program normally reads commands interactively when
run, you must cause it, when started running for such interactive use in the
most ordinary way, to print or display an announcement including an
appropriate copyright notice and a notice that there is no warranty (or
else, saying that you provide a warranty) and that users may redistribute
the program under these conditions, and telling the user how to view a
copy of this License. (Exception: if the Program itself is interactive but
does not normally print such an announcement, your work based on the
Program is not required to print an announcement.)
These requirements apply to the modified work as a whole. If identifiable
sections of that work are not derived from the Program, and can be
reasonably considered independent and separate works in themselves,
then this License, and its terms, do not apply to those sections when you
distribute them as separate works. But when you distribute the same
Release 1.20 Digium, Inc. Page 124