So I have a Nokia X2-01. Great phone. QWERTY. EDGE. Bluetooth. Upto 8 GB of extended data storage. And it looks good and doesn't feel too cheap.
Luckily it happens to be one of the phones that WhatsApp develops their Messenger application for. Really nice application. I've never been this happy with a chat application. It gives you the option to send out any type of data - text/voice/pictures/videos etc. Just wish more of my friends knew about and used it. It uses the contacts on your phone to tie you up with your friends. So no need to sign up and maintain any account of sort with them.
S40 doesn't offer a task manager by default. So you can't kill the process if you find yourself low on battery life. And closing the app from the menu is the S40 equivalent of run-in -background-all-the-freaking-time. S40 doesn't even have a connection manager that you can use to switch off the data connection. The only other option is to put your phone into in-flight mode, which is like running low on fuel in the middle of traffic, and turning off the engine, and hoping that Newton's First Law will help you get where you need to go.
Here's the fix. Navigate through to the entry for WhatsApp in the extras menu where it usually lands up. Apps > Extras > WhatsApp
Use the left selection key to bring up the context-sensitive options menu. Choose 'Delete'... Don't panic!
It will ask you whether you are sure you want to delete WhatsApp. Choose Yes.
Then it will double-check with you: "Are you sure you want to Delete WhatsApp?" Wait for a few seconds like Every-Reality-Show-On-TV-Judge-Eliminating-A-Contestant-At-The-End-Of-Every-Episode-Ever as you ponder your decision... And choose not to. Applause.
The EDGE connection icon should disappear (unless you have something else keeping the connection open). But there's a side-effect to this, I guess when this happens, the process forgets to close open file handles, because of which when you try to open the extras folder, it gives an error stating the filesystem is busy and to try again later.
Switch off and switch on your phone, and you should be good.
Hope this helps you. (Or just get a better phone. Even an S60 phone should be better than this. Since it comes with separate connection/process managers.)