that's already managed on the provider side!?

Or do you mean a program to manage the settings? On a "per line" solution? That would mean to implement all call-divert-frameworks like all cellular, all SIP, skype, gtalk, gvoice, and so on...

For cellular the codes are available at your SIM but the framework seems to have some bugs as far as I know from following the bugtracker.

My SIP settings I can change online, or directly at and just for my dect (means I change the setup for actually being connected, what happens when offline is set at the provider homepage).