I've really been having a hard time connecting using KPPP since I installed Slackware 14.0 last week (yes, I know 14.1 was released just around the same time!) Anyway, after much fruitless googling, I finally came across something that suggested that Network Manager might be the problem. Of course Network Manager relies on Modem Manager for detection of modems. So I uninstalled Modem Manager, and lo and behold, problem solved! I hope I'm not being premature here, but thus far, it seems to me that there's some kind of conflict between KPPP and Modem Manager. Has anyone else experienced this?
P.S. Just uninstalled Modem Manager from my Mageia partition. I'm able to connect just fine so Modem Manager wasn't necessary after all. I also notice that Modem Manager is a bit of a CPU hog. IMHO, Modem Manager still needs a lot of work!

Network manager since then has been updated. As far as what is causing the issue with KPPP and Modem-Manager, it could be a resource conflict rather than direct problems with KPPP and Network-Manager.

However, have you attempted to disable the Network-Manager daemon from starting up prior to using KPPP?

Thanks Reaper.
It was, as you say, a resource conflict between KPPP and Modem Manager. Yes, I'm aware that Modem Manager has been updated and I had half a mind to build and install the latest version, but since KPPP is working so well I don't think I'll be doing that. The Network Manager daemon is running and I'm hoping to test it on a wireless or wired network the first chance I get. But mainly, the problem was Modem Manager.