I am using Nokia 6680 phone with 2.04.15 version.In doing voice calls
I am facing the following difficulties.
1)redailing not working
2)calling through the entries enterd in phone telephone directory is not allowing.
 some times the above the above two items are working for few times if
I swich off and on my phone and later not working.I noticed that many
other users of the same model phone are facing the same problum and
told me as software problum
 Please tell me  exactly what to do to solve the problem and where the
things are available

In order to get the software upgraded you must take your phone to an
authorised Nokia service centre, if the phone is under warranty they
should do it free of charge.

Im not sure which country you are from but your local Nokia site
should have something like this on the Nokia UK site.

http://www.nokia.co.uk/nokia/0,,33684,00.html

Hope this helps.