The visible change is the name of the modules, they are prefixed with "db_" (e.g., myqsl module is now db_mysql). You have to change the loadmoule and modparam lines in your config file. The "db_url" parameter from different modules does not need to be changed, DB API takes care of prefixing with "db_". See more at:

 http://lists.openser.org/pipermail/users/2008-February/015735.html

 Internally, many common functions where unified and moved to core, making the maintenance easier. Work is still in progress, other enhancements are to be done in the near future.

As a side note, worth a mention the introduction of shared variables in configuration script. These are variables whose values when changed are visible at once across all OpenSER processes. They are exported by the cfgutils module:

 http://www.openser.org/docs/modules/devel/cfgutils.html