there are some ways but most are rather complicated, also since sega.net started charging $10 US a month to play all online games (except PSO v1, thats the only game that is still free now) the only thing a free isp will do is let you surf on your DC for free, and in that case you might as well stick with your PC for that
now if i could only remember the website that covered free isp's for DC!!
*note:*look at the sidebar on the left where the links to different pages of the site are supposed to be...you may not see them because the link colour is the same as the background colour so just highlight then click)
Juno works great and is pretty easy to set up. Go to dreamcastfun.com to do it. You need a PC to set it up (if you dont use PC that is...go to the library.) Once you get the info, you can use juno for pretty much anything that can go online. As for games that play onlin, right now you can play all of it free except for the games made by Visual Concepts (the sports games and Ooga Booga), otherwise the rest should still be free.