I'd say "ignore them". I'm not well-versed in python-dbus, not at all, but D-Bus services can have introspection data attached to them and programs/people can query this introspection data to see what methods et al. a service provides. Python-dbus tries to "make it easier" for the programmer by querying the service to see what services it provides and the data types of the return values of a method call.
As you saw, the Phone.Net interface doesn't implement the Introspectable interface so it cannot be asked to list the methods etc. it has. You may be able to find a way to stop python-dbus from asking but I wouldn't bother for two reasons:

• Who's gonna run it from the console, anyway?
• "Don't fix it if it's not broken." - I mean, querying the services works and you get the information that you want, right?