Calla lilies propagate quite well from harvested seed pods. Before attempting to plant a seed in soil, place several pods between damp paper towels on a plate, and put them in a dark, dry place. Within a few days, those most likely to succeed show signs of growth.
CallaLilyGuide.com recommends discarding weaker pods. Plant the stronger seeds in potting soil in a safe environment away from mice and birds, and water moderately to avoid root rot. Once the seeds demonstrate growth, again remove the stragglers. Discard the soil used for the preplant stage, gently wash the roots of the lilies to eliminate any bacteria, then place them in containers filled with fresh soil or plant them in the ground.