we use wishlist member too…  they work wonderfully together…

are you sure you mean ‘subscribe’ them to forum?  not following…  users can auto subscribe to topics they post in their sp profile…  but you cannot subscribe to the whole forum – that’s what RSS is for…

are do you really mean access the forum?  there is not a separate user db for simple press… as a plugin for WordPress we just sit on top of the wp users and database… if you are logged into wp, you have access to the simple press forum installed…  you can of course set different permission levels for users on different forums using sp usergroups and permission sets…

if you are using wishlist for varying levels of access, this will work with sp too… you can map a wp role to an sp usergroup on forum – options – member settings…  so with wishlist when you map a membership level to a wp role, they can also get a usergroup in the forum…  and if they get new membership, they can get differing permissions on the forum…  the only kicker is that when you do the mapping of wp role to usergroup, it takes effect from that point forward. any existing users need to be manually mapped on forum – usergroups – manage usergroups…

if you meant something else, please explain further…