There are still a very few dial-up BBS in existence, but don't expect them to last much longer for practical reasons: First of all you need to have one locally because of the calling cost (and I doubt there are more than 20 worldwide as we speak), then telephony is switching to voip all over the world and in many countries POTS is already history. So there's really no point maintaining a dial up BBS that receives 5 calls per year at best (yes, those are the numbers).
Most SysOps who still run their BBS (including myself) adapted to modern era, which means adding a telnet -> FOSSIL layer and made their BBS available over the internet through telnet or a web page plugin. Although a BBS nowadays is of no practical use, at least a much larger audience can be addressed so there is a meaning in keeping it running as an exhibit.
Just to make something clear for people who have no prior experience with BBS, accessing one over the internet doesn't ruin the experience. You just skip the dialing part, but after that the experience is authentic. Even proper modem speeds are emulated, you'll be seeing ansis loading at dial-up speed. So if you're not mostly interested in the actual dialing-up but in seeing the real thing, https://www.telnetbbsguide.com/ has a list of BBS you can connect to. Start with mine 🤣
(btw, Wildcat is just one BBS software, there are many more the BBS scene used)