Pressing button "Activate" on the netcfg panel fails to activate ppp interfaces. It seems that netcfg tries to execute /etc/sysconfig/network-scripts/ifup /etc/sysconfig/network-scripts/ifcfg-ppp0 in wrontg envinoment since I start ifup ifcfg-ppp0 manually (being in the directory /etc/sysconfig/network-scripts/) ererything goes just fine.
Thank you for a very good bug report; it made it quite easy to find and fix the bug. It will be fixed in the next initscripts release. In the meantime, you can use rp3 or usernet to control the interface, or you can use ifup ppp0 and ifdown ppp0 to bring your ppp device up and down from the command line.