The update for both iPhone and iPod Touch users can be downloaded by connecting the devices to a Mac or PC equipped with iTunes. iPhone users will receive the update for free.
First announced in March, the update is the largest to be issued for the iPhone since the 2.0 software was released last summer.
Among the new features are the additions of voice memo recording, multimedia messaging and the addition of Apple's Spotlight search software. Developers have also been given new tools with the update, adding abilities such as push data updates and access to iPod libraries.
The company has also tied a security update into the new software which addresses vulnerabilities which could allow for attacks that steal data or remotely executie malicious code on a targeted device.
Apple is issuing the software update just days before the new iPhone 3G S model is set to debut in the US. In addition to increased storage capacity, the new handset will sport a faster processor and more memory.
The hardware updates will offer faster performance and the ability to record video on the device.