Microsoft could re-think plans to phase out its Windows XP operating system by June 30 if customers show they want to keep it but so far they have not, Chief Executive Steve Ballmer said. "XP will hit an end-of-life. We have announced one. If customer feedback varies we can always wake up smarter but right now we have a plan for end-of-life for new XP shipments," Ballmer told a news conference on Thursday. Ballmer said most retailers sold computers with Vista, the latest version of its Windows operating system, and most consumers were choosing to buy Vista. Some consumers have complained they were unable to buy XP at retail stores, or as consumers. They say that in order to get XP they must buy their computers as small businesses. "In the business environment, we still have customers who are buying PCs with XP" because information technology departments often have to work with old machines, Ballmer said. Vista requires high-speed central processing units installed only in newer machines.