We are still actively working on the spam issue.
SDF (full name: The SDF Public Access UNIX System) is a service that is marketed as a "UNIX-based Social Network". In reality it is a UNIX shell account that has a number of features. Founded in 1987 as The Super Dimension Fortress Macross --an Anime-centric BBS-- it has evolved to a full-featured loan shell. Very popular among Cyberpunk communities (like Lainchan), it has a wide cariety of users from all over the world.
To "validate" your account, you need to send by mail $1 to their HQ in Seattle, WA. This is to prevent spam and help with server costs. For another USD, you can get DF stickers. There are membership levels above this, such as ARPA for a single $35 fee.
To log in, you ssh into your account and then have access to the SDF's TTY.
Basic account features
The SDF server also hosts internet services for subscription rates. These include Dial-Up, DSL, and an ISDN connection. VoIP is avalible to all users, but to make calls on the Public Telephone Network, you need to be an ARPA member. This VoIP service is provided as an extension of C*NET.