OK - you can still do this with OS 4. I have a Pearl running 4.5 and here are the steps:
1. Click on the Profile icon on the home page
2. Click on "Advanced"
3. Press the BlackBerry button and select "New Profile" and create a profile for the person you want a special tone for and set the . I used to name the profile with their name.
4. Set all the different setting (calendar, Messages, Phone, etc.) for the tones you want to use for this person.
5. Click the BlackBerry button again and SAVE your profile - this should take you back to the list of sound profiles.
6. Click the BlackBerry button again and this time select "New Exception"
7. Give the Exception a name (again, you can use the person's name or whatever you like here)
8. Scroll down to the "From:" field and press the BlackBerry Button
9. Select "Add Name" from the pop-up dialog
10. Select the contact you want to apply this special profile to and press the trackball to select. Their name should now show in the "From:" field
11. Scroll down to "Use Profile" and click the trackball. This will display all the sound profiles you have.
12. Scroll down to the new profile you just created and click the trackball to select it.
If you want a custom phone tune for this person, check the "Custom Phone Tune" box and then scroll to the tune showing on the right. Click the trackball when you're on it and it will show you all your ringtones to select from.
When you're all set, click the BlackBerry button again, select "SAVE" and you should be all set.
Again, this is using OS 4.5 so if you have something earlier than that, I don't know if this will all work for you.
Hope that helps!