We have studied the transition to phase synchronization in the system of two coupled periodically driven pendulums. For the case of identical units, the coupled system has an infinite number of invariant subspaces. The synchronization-desynchronization transition is at the blowout bifurcation which coincides with the hyperchaos-chaos transition. On-off intermittency and intermingled basins of attraction can be observed close to this transition. For the case of nonidentical pendulums, the synchronization-desynchronization transition occurs far beyond the hyperchaos-chaos transition. The basin structure and the statistics of the accompanying intermittency are different from those for identical units.