According to the CME Features Roadmap, the night service bell is now supported on SIP phones.
The documentation on the Cisco website would have you believe that it is possible to create a Night Service button on SIP phones, there are at least two references to this in voice register pool and voice register template:
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucme/command/reference/cme_cr/cme_f1ht.html#wp1278238710
feature-button (voice_register_pool)
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucme/admin/configuration/manual/cmeadm/cmelabel.html
Configure Feature Button on a Cisco Unified SIP Phone Line Key
Despite this, even with CME 11.6 it seems that the NiteSrv option (and several others listed above are really not available). Is there something I'm missing or are the docs wrong?
cme(config-register-pool)#feature-button 2 ?
Cfwdall Call forward all (N/A on 99xx and 8961 phones)
ConfList ConfList (N/A on 99xx and 8961 phones)
Confrn Conference (N/A on 99xx and 8961 phones)
DnD Do not Disturb
EndCall End call (N/A on 99xx and 8961 phones)
Gpickup Group Call Pick Up
HLog HLog
Hold Hold (N/A on 99xx and 8961 phones)
Meetme Meetme
Mobility Mobility
NewCall New call (N/A on 99xx and 8961 phones)
Park Call Park
Pickup Call Pick Up
Privacy Privacy
Redial Redial
Trnsfer Call Transfer (N/A on 99xx and 8961 phones)