It seems that at one time you opened Skype and when you closed it, you have the ability to leave it running in the background. I know that much, but I'm not a regular user of Skype of the phone. As far as how it works to answer, it would depend on the settings for the app. You may get quicker responses if you head over to a Skype forum, but someone else here may be a regular user and have more information. It does not react the same as a regular phone call, but then, I would imagine that if someone needs to contact you in an emergency, they would use your regular phone number, which is much easier to answer. You might also wish to experiment with Skype during the day to see how it appears on the lock screen, and check the app settings in Settings>Notifications to see how it is setup to appear.