After nearly 3 years of service, Atlus will be shutting down Demon's Souls' North American servers starting late next month.
Atlus insists that this will not affect the game's single player mode, although the publisher did not say if that includes the ability for players to leave notes and hints online.
It's also safe to assume that this might mean that certain stones which call in friends in time of need may no longer be useable, but this was not confirmed.
The servers will close on May 31 at 11:59 PM PST. As Demon's Souls' online mode takes its final bow, Atlus will be holding two World Tendency events from May 1-15 and May 16-30, voted on by fans.
Source: Game Informer