It's available on the update sites, so I tried it out today.
My modem at some time in the past changed from being on /dev/ttyS4 to /dev/ttyS14. Wtih
the new kernel it reverts to being ttyS4, which required editing a few places to get it working
again. Specifically /etc/sysconfig/network-scripts/ifcfg-<name of ISP> and the name of the
lock file in the advanced tab in modemlights.
Then it seems to have broken packet forwarding. One might argue that trying to packet forward
through a dialup ppp connection is broken in principle - but when that's all you've got, you make
do with it. Anyway I did the iptables commands by hand and it started packet forwarding but seemed
to be very sluggish at it. So for now I have reverted to the last 2.6.12 kernel. But I'm leaving
2.6.13 up on another machine that doesn't have a modem - everything seems to more or less work