Asterisk 1.6.0 has now been officially released. One of the questions that is going to come up over time is how to port custom code that was written for older versions of Asterisk up to Asterisk 1.6.
For Asterisk 1.6.0, we included a document that describes every C level API change between Asterisk 1.4 and Asterisk 1.6. For more information, see the file
doc/api-1.6.0-changes.odt in the Asterisk 1.6.0 tarball.