11 volumes have been released so far, with a free access after inscription. The first three volumes Pompeii are now on line, on Arachne (where some other Pompeian books are also available):
Inscriptiones parietariae Pompeianae, Herculanenses, Stabianae (CIL IV, first volume by R. Schoene).
Inscriptionum parietariarum Pompeianarum supplementum. Inscriptiones parietariae et vasorum fictilium (Mau's supplement, CIL IV, suppl. 2).
All of this is more than useful, even some inscriptions might have been revised in the fourth supplement published last Dicember.