The Enternet 300 connection software includes the PPPoE protocol, which is nowadays required by many xDSL providers, used mostly for residential ADSL connections. In a sense, it makes the ADSL connection authentication process somewhat dialup/ISDN-like.
Here's some reading on the reasons why ISPs do this nowadays: http://www.vicomsoft.com/knowledge/reference/pppoe.html
I personally hate using Enternet; instead I prefer using RASPPPoE. (http://www.raspppoe.com