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.
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: https://src.fedoraproject.org/rpms/asterisk.
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