The evolution and collision of dark solitary waves (solitons) appearing in
cigar-shaped Bose-Einstein condensates with repulsive atom-atom interaction
are here considered using a Boussinesq-Korteweg-de Vries description. We p
rovide theoretical predictions and computer experiment evidence about their
phase shifts or change of trajectories, in the space-time plot, correspond
ing upon collisions. Details are also given about a suggested experiment th
at could assess their genuine solitonic nature.