I have an iPhone 3GS. If I update to the new iOS software update from iTunes will I still get multi-tasking and many of the other features it has to offer?
The software update is free for everyone. As a 3GS owner you will get all the features. It will be released next week, on the 21st. Just connect your phone to iTunes, sync and back it up one last time, and then on the summary screen hit "check for update."
Absolutely. Since you have the 3gs, one of the latest models besides the iphone 4, you are eligible for a free update to the new ios. update it. You will be able to receive the different features that comes along with it such as multitasking, etc.