For those who wish to test Asterisk 1.8.0, Fedora 13 i686 & x86_64 RPMs for Asterisk 1.8.0 are built and available in the mss-testing channel of the Fedora & Enterprise Linux RPM Repository.

$ yum --enablerepo=mss-testing ...

It does not appear that Fedora will ship its own Asterisk 1.8.0 packages for Fedora 13 or 14, though you can keep an eye on the status here:

The packages built here are built from the same spec and patch files with the exception that the libpri-devel version requirement was reduced from 1.4.12 to 1.4.11 since Fedora 13 does not contain the 1.4.12 version.

View the original Asterisk 1.8.0 release announcement