To use these devices you need the program ipppd , which you have to configure. You have to start ipppd once after the modules are installed. A single ipppd can handle all devices at once. If you want two PPP connections at the same time, you need to bind ipppd to two devices, etc. It is very important to set up the authentication information properly.
Improper authentication is probably the most frequently reported problem on the mailing list.
Please, work through section pap completely yourself, before asking others for help. However, normally one ipppd is meant to handle all traffic, so it is highly recommended to only set up several ipppds if their configuration has to be different. When giving the option defaultroute , then you can wait a few seconds, then check whether the default route exists. In either case, the connection is up. Next time, configure ipppd without these unused options.