The iPhone 3GS was first introduced by Apple in 2009 at an event called the WWDC 2009 which was held at the Moscone Center in San Francisco. The improvements from the previous device primarily consist of faster performance, like a higher resolution camera, that now supports video recording, support for 7.2 Mbit/s downloading (although the upload speed remains at 384 Kbps due to Apple's choice of not implementing the HSUPA protocol). The device was released on June 19, 2009, for the United States, Canada and six other European countries, on June 26 for Japan and Australia, and July and August of 2009 for the rest of the world.
The iPhone 3GS uses the same Mac OS based operating system named iOS (primarily named iPhone OS) that was implemented on all other models. The iPhone can execute a great number of applications, as long as those applications are checked and approved by Apple itself, and obtained through their online application store called AppStore. Doing otherwise can cause sever software malfunctions that will not be covered by the warranty certificate. The reason for which the name was changed from iPhone OS to iOS is that the operating system was no longer exclusive for the iPhone, as it started to be implemented on the Apple iPad tablet computer and the iPod Touch portable media player. The only thing these three types of devices have in common besides the operating system is the fact that all three have the control built around their main input, which is a multi touch based 3.5 inch liquid crystal display intended for bare finger-usage.
Because it was intended for bare finger-usage, people may have problems using normal gloves of styluses because the interaction between them and the display is not able to create the needed amount of electrical conductivity for the screen to record it as a touch event. But you can always buy some special gloves or styluses which will work just fine.
The fact that most improvements from the last versions regard speed can be deducted from the device's name, iPhone 3GS (the name is basically that of the last model, iPhone 3G, but with an extra "S" which stands for "speed"). However, there are some software changes also, and improvements that at that time were exclusive for the iPhone 3GS, but faded when the iPhone 4 appeared, such as Voice Control, which allows a user to give the phone control using his voice. The phone has a series of commands stored which allows it to identify the requested task.