We can use the Single Number reach feature on the call manager to archive this, below is for reference :
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/9x/uc9x/mobilapp.html#wp1237920
We need to configure the remove destination (ie the mobile phone number), associate this to local extension on call manager.
Use the below reference for complete configuration :
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucme/admin/configuration/guide/cmeadm/cmesnr.html
-Rohit