According to Applie insiders, multi-tasking will be just a part of the iPhone (iPod Touch as well) 4.0 operating system update. Even though the release date is another five months away, rumors are certainly circulating about it. I am guessing the 4.0 will be released with the latest iPhone, much as the 3.0 operating system update released when the iPhone 3GS was introduced this past June.
This seems mostly important from the perspective of the coming-next-month iPad, which will lack the critical feature that the smaller versions have. Outside of a few key apps, you are only allowed to run one application at a time. Now this obviously excludes phone usage, playing music with the iPod feature, instant messenger applications, text and mail messaging. However, the goal will be, from what I read, to have all applications able to stay open. I become disgruntled when I am using the Maps feature for GPS routing, and I receive a text message than I need to respond to, or a phone call I need to make.
The new iPhone will also see a boost to a 5 megapixel camera (whereas the 3GS sports a 3.2MP and the regular iPhone 3G a 2MP).