I recently managed to connect to office communicator under linux.
First I installed pidgin-sipe and configured my account. But something seemed to be wrong with the ssl communication. So I copied over all ssl certificates from pidgin:
cd ~/.purple/certificates/x509/tls_peers && sudo find . -type f -exec
cp {} /etc/ssl/certs/{}.pem ;; sudo chmod a+r /etc/ssl/certs/*
Then I added “NSS_SSL_CBC_RANDOM_IV=0” (without quotes) into /etc/environment and restarted X by logging in and out.