Hello Marco,
It is not possible to get an login button for Hoteling on Cisco phones right now. It is possible to login on a phone as Hoteling Guest by calling to the voice portal. With Cisco Phones EM en ACD are not gonna work.
In Broadsoft you have to make the Phone wich you use to login a Hoteling Host Phone you need a Premium licence for the Hoteling Host. The Hoteling Guest also needs a Premium or Bussines licence.
You can take a look at the Routit Help portal there is a video voor Hoteling on a Polycom Phone.
Or on Youtube
http://www.youtube.com/watch?v=MAZKPW3GkDg
Kind Regards