  If the massive neutrinos are identified to be the Majorana particles via a
convincing measurement of the neutrinoless double beta (0\nu\beta\beta) decay,
how to determine the Majorana CP-violating phases in the 3 x 3 lepton flavor
mixing matrix U will become a desirable experimental question. The answer to
this question is to explore all the possible lepton-number-violating (LNV)
processes in which the Majorana phases really matter. In this paper we carry
out a systematic study of CP violation in neutrino-antineutrino oscillations,
whose CP-conserving parts involve six independent 0\nu\beta\beta-like mass
terms <m>_{\alpha\beta} and CP-violating parts are associated with nine
independent Jarlskog-like parameters V^{ij}_{\alpha\beta} (for \alpha, \beta =
e, \mu, \tau and i, j = 1, 2,3). With the help of current neutrino oscillation
data, we analyze the sensitivities of |<m>_{\alpha\beta}| and
V^{ij}_{\alpha\beta} to the three CP-violating phases of U, and illustrate the
salient features of six independent CP-violating asymmetries between \nu_\alpha
\to \bar{\nu}_\beta and \bar{\nu}_\alpha \to \nu_\beta oscillations. As a
by-product, the effects of the CP-violating phases on the LNV decays of doubly-
and singly-charged Higgs bosons are reexamined by taking account of the
unsuppressed value of \theta_{13}. Such CP-conserving LNV processes can be
complementary to the possible measurements of neutrino-antineutrino
oscillations in the distant future.
