I have been using Twitter to sign in to Nokia Services, why don't I see the Twitter sign-in option on my Nokia Lumia with Windows Phone 8?

Your device doesn't support signing in with the identity provider you are trying to use, check if you have the latest software on the device. Conversely, you can sign in with your Nokia password if you have one. If you don't have a Nokia password, then you can select the link I don't know my password from the sign-in page and create a Nokia password.