Delivery times quoted on Apple’s online store for new iPhone 4 orders slipped to 1-3 business days this week, suggesting inventory may be diminishing. Orders placed on Apple’s U.S. website had previously shipped within 24 hours of being placed. With an announcement regarding Apple’s fifth-generation iPhone expected within the coming weeks and a launch to follow in October, iPhone 4 supply is likely beginning to run low. Apple may also launch a new low-cost version of the iPhone 4 alongside the iPhone 5 next month, so the current model could very well be near its end of life (EOL). Additionally, shipping quotes on Apple’s site historically grow longer as new product launches approach, as noted by several reports.

UPDATE: As of Friday morning, Apple has removed estimated shipping times from its order page, replacing them with an “In Stock” note.