I tried to get my N73 unlocked a few weeks ago and found this site below for £10
http://unlockphone.org.uk/
DON'T USE IT! They say it will unlock with the cable that comes with the phone, but once you've paid they say you need to buy the DKU5 cable and NOT the one with the phone.
I explained this and asked for a refund to simply be told "NO we don't do refunds!". I tried getting my money back through Googlecheckout who told me to go to Mastercard and Mastercard are being nobs so spent as much on the phone as it cost me for the unlock.
Just a word of warning, plus every email from them comes from a different AOL or Tiscali address!