Now, this topic has come up several times in the Facebook site of the Vodafone 555 Blue and I would like to answer it here instead of the Facebook page.
The simple answer is: you can not log out of Facebook on Vodafone 555 Blue.
This is intentionally done this way and there is actually no need to do so. It may be the case that a user has not really unerstood how the device works with Facebook when the desire to log out comes up. So let me try to explain what is actually happening:
When you login to Facebook, we synchronize your contacts, wall, messages, newsfeed and albums. By default, the device will now connect to the network every 20 minutes and check for updates (like new messages and notifications, etc.). You should have received a suitable data tariff from your local Vodafone country with the device so that this data traffic should not be of any concern to you.
If you still want to save on the amount of data the devices requires, we have implemented several mechanisms that allow you to control your data spend without requiring you to sign out of Facebook. Please go into the “Settings -> Facebook settings” menu. Then go into “Background updates” and put all three settings to “Manual update”. This will switch the device to complete manual mode and it will not fetch any updates in the background anymore.
Please note that this means that you will not receive any Facebook messages, notifications or any other updates anymore. You will have to manually refresh by e.g. using the f-key (set to “Refresh Facebook data”).
If you are not worried about data consumption but you care about privacy only, then you can protect the device with a lock code from unwanted access. In this mode, you will have to enter a 4-digit code every time you unlock the device. Please go into “Settings->Security->Activate phone code” to turn this feature on. The default code is “1234” and you can change it in the menu below (“Change phone code”). You can obviously always use this feature, regardless of your data prefetching settings.
Lastly, if you want to use the phone with a different Facebook account, you can simply go into “Settings->Facebook settings->My account” and sign in with a different account. Please note: This will not immediately clear your phonebook and other settings. So if you want to completely change the account on the phone (e.g. sell the phone to someone), then you will have to perform a factory reset to wipe all your data. Just turn off the phone. Then keep the “v” key pressed while you turn it on again. Then follow the instructions on the screen to clear the data.
I hope you can see that there simply is no need at all to log out of Facebook. You can always log in with a different account, turn off all background synchronization to control your data spend and protect the device from unauthorized use.