From the settings menu, what's "Enter code to remove operator lock"? I've tried 4 various passwords and could get it.

try out 12345

My bad, misunderstood the question with Device Lock code !

the purpose of the operator lock code is that if you have taken your N900 under a contract and want to unlock the phone so that you can use any simcard , you need to enter the operator code. This is given by the cellphone company when you complete your contract or after 4-6 mths of using the phone.

I found one thread on this .. http://talk.maemo.org/showthread.php?t=58232

I can't find that setting. My device is sim-free. Is your device locked to a particular operator?

EDIT: I didn't realise you meant the drop-down menu. I have found it now.

I suppose it was included to cover the case where devices are locked to an operator. As far as I'm aware, no such devices exist.

My device is not locked to any operator. Didn't want to try the 5th time and risk getting the whole thing locked up. But hope to find out just in case one day I accidentally press the wrong thing.

A network lock, known by many names including SIM lock, simlock, or subsidy lock, is a technology that wireless communications carriers use to prevent the mobile phones they sell from being used on another network. Cell phones can be locked to a particular country, network, or subscriber identity module card. A locked phone is typically sold to customers at a discounted price, since the carrier expects to earn income from the customer by providing wireless service to the phone. An unlocked phone able to use any service provider sim cards. Most of the mobile phones have only 5 chances to enter wrong unlock codes. You must get correct unlock and enter or your phone permanently locked with current service provider. So you can get unlock codes from your current network provider or any online unlocking service providers. Mobile-Unlocker.com is one of the trusted unlocking service provider for most of the GSM mobile phones world wide..