In my phone instead of unlocking screen by providing "symbol", I'd like the phone to unlock to most of my applications without the "symbol". But for selected important applications (eg. gmail) I'd like it to ask for the symbol. It would be useful eg. when I borrow my phone someone to play games. Is there application which would help me to achieve something like that?
Sounds like you are looking for an app which allows you to password-protect other apps. There are many on the Market, but I haven't used them so cannot comment on their reliability.