You mean, following down the path that Palm OS devices used since first released in 1996?
That said, neither Palm OS or Newton OS could multitask. Android and the iPhone OS seem to have found a very elegant approach to that particular problem without compromising the user experience.
The Palm had 4 threads, only one of which was available to the developer. Another was used for comms and a third for graffiti processing. I don't think the last one was allocated.
The Newton had at least two threads -- comms in the background were needed even in those dark ages.