Can I use AirDrop on the iPhone 4 / 4S?
Apple has included AirDrop in iOS 7 to simplify the process of sharing files and other information between iPhone users in the vicinity. Despite the fact that iOS 7 can be installed on the iPhone 4 and the iPhone 4S, some features in the latest firmware are not available.
AirDrop is one of these features that is only accessible on the iPhone 5 or later. This means that for now, iPhone 4 / 4S users cannot use AirDrop to share files, even with iOS 7 installed.