Last week I was surffing the web and stumbled accross this post in a Brazilian forum (it is Brazilian Portuguese) explaining how to set up a DSL connection in Plasma NM. Basically Plasma NM really works with DSL, which is great, but there is a catch: you need to disable the auto-connect option for the wired connection that uses the same device that the DSL connection uses. Explaining: DSL works over ethernet (more common), wifi, and maybe over other devices. When the device (ethernet) is meant to be used with DSL you must disable the auto-connect feature in the wired connection associated to that device. First create a system DSL connection:
In the Ethernet tab restrict the connection to a specific ethernet device. If you have more than one ethernet device do not be afraid, the "eth0" below is just an user-friendly way to select the device, what Plasma NM really uses is the device's MAC address. If for example you have eth0 and eth1 in your system, then you restrict to eth0 but for some reason the system swaps eth0 for eth1, Plasma NM is smart enough to see that and it will automatically change the configuration to eth1.
Save the configuration by clicking on the Ok button and go to the Wired tab in Plasma NM's kcm (k control module):
Click on "Edit", the edit dialog will appear. Go to the connections's "Ethernet" tab and disable "Connect automatically" and check "System connection" to allow the system (NetworkManager) to use the connection without you need to open a KDE session first:
Save the configuration by clickling on the Ok button and try to connect. You can check if it is connected in Interface Details for the wired connection (I got this screenshot from the forum, that is why it is in Brazilian Portuguese):
Notice the "Nome do sistema" field (System name) showing "ppp0", that means the connection is really active.
For some reason nm-applet does not require changing the wired connection configuration, which sounds reasonable. But without a connection to test it will take me time to figure out how to make that work. Until then DSL users can use the configuration above.