UPGRADE.txt

Information for Upgrading From Previous Asterisk Releases
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Manager:

* The CallerID fields across Manager events have now been made more
  consistent. CallerID Number will be sent as CallerIDNum and CallerID
  Name will be sent as CallerIDName wherever used.

AEL:

* Macros are now implemented underneath with the Gosub() application.
  Heaven Help You if you wrote code depending on any aspect of this!
  Previous to 1.6, macros were implemented with the Macro() app, which
  provided a nice feature of auto-returning. The compiler will do its
  best to insert a Return() app call at the end of your macro if you did
  not include it, but really, you should make sure that all execution
  paths within your macros end in "return;".

Core:

* The 'languageprefix' option in asterisk.conf is now deprecated, and
  the default sound file layout for non-English sounds is the 'new
  style' layout introduced in Asterisk 1.4 (and used by the automatic
  sound file installer in the Makefile).

Applications:

* The voicemail configuration values 'maxmessage' and 'minmessage' have
  been changed to 'maxsecs' and 'minsecs' to clarify their purpose and
  to make them more distinguishable from 'maxmsgs', which sets folder
  size.  The old variables will continue to work in this version, albeit
  with a deprecation warning.
* ChanIsAvail() now has a 't' option, which allows the specified device
  to be queried for state without consulting the channel drivers. This
  performs mostly a 'ChanExists' sort of function.
* SetCallerPres() has been replaced with the CALLERPRES() dialplan function
  and is now deprecated.