This was done on a debian jessie box.
- Install pidgin and pidgin-sipe: sudo apt-get install pidgin pidgin-sipe
- Start pidgin
- Add a new account — choose Office Communicator
- Set Username: email@example.com; Login: ad.umu.se/abcd01234 and give your password.
- Done! It works for making and receiving calls. Not sure about other features.