Return to where I was...

[Shaolin Hu]

If user press a key that launches a standard palm appliction, say, the
calculator, from within my application.
Is there a way I can make it to return to my application at exactly where
they left off.
I have been asked several times by my users to have this feature and I have
been telling them 
it is impossible, am I right?  Thanks.
Shaolin Hu