Keeping ones phone's quality intact is kinda a difficult thing to do but if you follow the tips below, you probably make your phone last. This trick is meant mostly for s60 phones, but s40 users can still use it. Some of the tips are outline below;

1. Never install any mobile antivirus applications.

2. Avoid installing any autorun mobile applications.

3. Avoid installing any animated themes.

4. Do not install any received file if you don't know the sender.

5. Always turn off your bluetooth
if not in use.

6. Do not install any ram boosters.

7. Set your LOGS to 1 day.

8. Do not install any screensaver applications.

9. Always clean your
LOGS.

10. Install your mobile theme in phone memory (do not install many themes, only 1 that your
gonna use)

11. Set your messaging to phone memory unless you are receiving files via bluetooth.

12. Do not store any media files in phone memory.

13. Do not install any
softwares in phone memory.

14. Delete all unnecessary applications and files.

15. Avoid inserting your memory
card in other phone (vise versa) to avoid transfering of viruses.

*hope this tips are helpful.... goodluck*