With the new Apple iOS 5 you can customize more than just your ringtone and text tone. On previous iOS version you can customize only ringtone and text tone from the settings options. Now in new iOS 5 you can customize the alert tones for e-mails, voice mails, Twitter, and more. So from now onwards you can set your facorite alerts for you mail, twitter and messages.
With these steps you can customize your alert sounds
1. Go to Settings and choose Sounds.
2. Now on the Screen You can see lots of Alert options, from here you can choose ringtone, text tone, new voice mail, new mail, sent mail, tweet, and calendar alerts.
3. You can also adjust the volume of your ringtone and other alerts by using the slider above