Comment 8 for bug 589307

This Bug still exists on Lucid Lynx (10.04.2 LTS), amd64
[Jun 28 09:52:29] WARNING[24307] loader.c: Module 'format_mp3.so' was not compiled with the same compile-time options as this version of Asterisk.
[Jun 28 09:52:29] WARNING[24307] loader.c: Module 'format_mp3.so' will not be initialized as it may cause instability.
[Jun 28 09:52:29] WARNING[24307] loader.c: Module 'format_mp3.so' could not be loaded.

As a work around one can use the version from maverick:
https://launchpad.net/ubuntu/maverick/+package/asterisk-mp3

This module loads without a message, the file format shows up on core show file formats:

Format Name Extensions
------ ---- ----------
slin mp3 mp3
...