A Soulstone is a conjureditem that a warlock can create beginning at level 18 with the [Soulstone] ability that temporarily grants one player the power of self-resurrection or allows the warlock to battle-ress a dead friendly target. It is also a verb term for applying any type of soulstone to a target, as in "to soulstone somebody."
Patch 4.1.0 (26-Apr-2011): Soulstone can now be used in combat to resurrect a targeted dead player.
Patch 3.3.0 (08-Dec-2009): The cooldown on this spell and duration of its buff have been lowered from 30 minutes down to 15 minutes. Cannot be used in Arenas.
/Patch 3.0.2 (14-Oct-2008): Soulstone now generates a log entry indicating who casted and received a soulstone.
Patch 2.3.0 (13-Nov-2007): Soulstone's animated visual effect no longer appears around the warlock when the soulstone is used. It appears around the soulstoned target now.
Patch 2.1.0 (22-May-2007): Soulstones can no longer be used on targets not in your party or raid. In addition, the soulstone buff will now be removed if the target or caster leaves the party or raid.