Well, there was until recently the Cottonwood BBS:
http://cottonwood.servebbs.com/And it might be up again in a few years according to the website. This is a real BBS you can dial up from a modem.
Also, didn't someone revive Quantum Link as Q-Link?
It's more internet connection based, but you can log onto it with a real Commodore 64.
(checking)
...oh it looks like it might be offline as well. But here was a discussion about it in 2007:
http://www.lemon64.com/forum/viewtopic.php?t=24151
