How does Planning Poker work with a distributed team?

Simple: go to  PlanningPoker.com. Mountain Goat Software developed that website to offer it as a free resource to the agile community. A product owner, ScrumMaster or agile coach can log in and preload a set of items to be estimated. A private URL can then be shared with estimators who log in and join a conference call or Skype session. Agile estimating and planning then proceeds as it would in person