  Current induced precession states in spin-transfer devices are studied in the
case of large easy plane anisotropy (present in most experimental setups). It
is shown that the effective one-dimensional planar description provides a
simple qualitative understanding of the emergence and evolution of such states.
Switching boundaries are found analytically for the collinear device and the
spin-flip transistor. The latter can generate microwave oscillations at zero
external magnetic field without either special functional form of spin-transfer
torque, or ``field-like'' terms, if Gilbert constant corresponds to the
overdamped planar regime.
