Horse's mouth:
"The first ten Iridium NEXT satellites were delivered to a 625 kilometer (km) temporary parking orbit where they will be tested and exercised by Iridium over the coming weeks. Upon meeting testing and validation requirements, the satellites will then be moved into their 780km operational orbit and begin providing service to Iridium's customers. One-by-one, the new satellites will be positioned near a current generation satellite, each moving at approximately 17,000 miles per hour as testing begins. Iridium's unique inter-satellite communication links from nearby satellites will be repositioned to point to the new Iridium NEXT satellite as it prepares to take over service. Existing satellites will eventually be de-boosted and de-orbited."
http://investor.iridium.com/released...easeID=1007978