Funny thing I was looking for the same thing but came empty handed.

Anyone know how, you can fill us in.
I guess you just have to answer the phone, hit the speaker function, hit Home ... hit the apps you just closed and hope you can start from the same spot*

*Eg: when in "Internet" App, hitting home and re-opening it gets you to the same place but even though it is completely unnecessary the app automatically refreshes the page (which is annoying because it always takes a while to render, especially in low coverage areas).
Other examples, some apps just start from the beginning ... which is really frustrating if you hadn't saved/was at a critical moment.

(android has some things better than the N900, but you just cant help love the things the N900 does great)