Its my first post I love my N900 but I did not find anything on the internet about N900 being registered to a CUCM as a SIP phone so I did it and here is how I did if somebody is interested. On the CUCM. 1. Add a End-user (or use an LDAP user if CUCM i connected to LDAP) Use your standard User settings. 2. Add a phone Device - Phone - +Add New - Phone Type = Third-party SIP Device (Basic), Next 3. MAC Address* = Any MAC Not used or the N900 MAC Address (Settings/About product) 4. Use your default phone settings. 5. Digest User = Select the Digest user (see above). 6. Add directory number and use your default CUCM settings. 7. Click Save and Apply config. On the N900 1. Go to setttings - VoIP and IM accounts - New 2. Select SIP 3. Username = phone number@CUCM_IPADDRESS (I used the publishers IP) 4. Password = does not matter just put something 5. Click Advanced settings 6. Username (digest user see above) 7. Outbound proxy = CUCM_IPADDRESS (I used the publishers IP) 8. All other settings default and click Done For me I use the MAC adress of the N900 and I associate the phone to the user it is just nicer but you dont have to. Its also strange that the password does not have to be correct but I did that but as I said you dont have to.