What do you mean? That generically refers to being in a call and able to surf etc. Any 3G device on the 3G network should do that with ease. Only one I know of that will not and it is not a BB. Holding down the BB Menu key brings up the application switcher so you can go "Home" to launch something else or bring up another application that is already running.
Posted from my CrackBerry at wapforums.crackberry.com
Yes that is multitasking. Running multiple apps or programs in the background at the same time that you are using something else, or talking on the phone or texting... etc.