Main reasons for Caller ID not to work

1. Duplicate entries in contacts - by FAR the most common cause and unfortunately, the most awkward one to fix.
If the phone finds the same number against more than one name, it doesn't know which to use so, perfectly sensibly, it defaults to showing the number.
The only way to fix this is to remove duplicates from your contacts. Best way to do this would probably be in Outlook on the PC, but assuming you can't do that, then you have to find the numbers that aren't working a use the LATEST version of the Nokia Search tool to find the duplicate entries:
NOTE: when you search, use PART of the number to avoid problems with formatting: searching for +441234567890 will NOT find +44 123 456 7890 whereas searching for 789 would.

2. Using your international dial code instead of '+'
Not sure if this applies to all phones, but if you store your number using your county's international dial code (eg: 004412345678990 - WRONG) instead of the '+' sign (+4412345678990 - RIGHT), it can cause problems.

3. "(0)" area code prefixes
Only a problem if you synch with MS Outlook. When you specify a country in MS Outlook, it will insert "(0)" into your phone number after the country code - while somewhere in Redmond, Bill Gates cackles - so +4412345678990 becomes +44 (0) 12345678990.
You need to remove the (0).

4. 9 and 10 digit numbers
There has been one report of problems with 9 and 10 digit numbers where one size doesn't work with SMS and the other with calls.
I think you know what you should resort to doing if still cant sort out the problem..re-update fw!

Author: JeckTheHell from N95Users.com