I'm using google groups. Kind of defeats some of the joys of usenet
with a web front end. But it is free, and, while the default settings
are horrid it can be set-up to be threaded. So, if you're willing to
go the web route and ignore the sponsored links (no problem they're
off to the side) you get a mobile interface that allows you to get
group access from any old computer that is attached to the web...
Mixed, but workable and free.

-- Tom.