Google provides you a very good contacts manager. http://contacts.google.com
Google also gives you the ability to synchronize your phone contacts with the contacts on your gmail account. I found this
quick tutorial to do contacts sync on Nokia 5800 xpress music phone.
Now contacts on my Android phone (Google Nexus One) and Nokia phone (5800 Xpress Music) as always in Sync and backed up ;)
Steps of enabling the Contatct (only Contacts) Sync on Nokia 5800.
Go to Menu -> settings -> Connectivity -> Data transfer -> Sync -> New sync profile
In the 1st page put any name for the profile.
In the 2nd page select "1.2"
In the 3rd page select ONLY Contacts.
In the 4rth page type "Contacts" (without the quotes).
In the 5th page select "Internet"
In the 6th page type "https://m.google.com/syncml" (watch out for the "s" on "https")
In the 7th page type "Google" (capital ‘G’ is important)
In the 8th page put the user name of your account.
In the 9th page put the password of your account
Once you are over with the pages it will go you to "sync"
You will press options -> Change active profile -> The name of your profile
It's ready for you to try it!
Go to your contacts and press Options -> Synchronization -> Start
It is ready!!!!!
Note: At a time it syncs 50 contacts, so you may have to run it multiple times.