I think we all multitask to some extent which is not just task switching. Such as while watching a movie, we watch the visual scene (containing multiple objects) , listen to the soundtrack (music + voice), perceive the theatre hall's airconditioner temperature, all at a time. I don't feel it is just a very fast task switching. Its just simultaneous processing of several sensory inputs.
Talking or thinking while walking is another example of multitasking.
Breathing is another example of multitasking, we continually do it even when we do any other work. (Breathing is partly a voluntary action, we have voluntory control over it).
However doing certain types of work together, may be difficult for some and not so difficult for someone else.
For example I know a tutor (male) who can solve chemistry problems over a paper while receiving a phone call about another chemistry problem.
My mother can listen to my words while she teaches music via phone and can interfere the student on other end of phone making a mistake.
I know several female teachers who can write something while listening to something else.