The video below from SampleFive does a very good job of illustration the steps listed.
Verify Extension Mobility Service is Running
Note: I've also seen where multiple call managers are being used to register phones, however, the Cisco Extension Mobility Service is not active on all servers. Watch out for this.
- From the Navigation menu select Cisco Unified CallManager Serviceability
- Select Tools > Control Center – Feature Services
- Make sure that the Cisco Extension Mobility service shows status Activated
Configure Extension Mobility Service
- From the Navigation menu select Cisco Unified CallManager Administration
- Select Device > Device Settings > Phone Services
- Click Add New
- In the Service Name field, type Extension Mobility
- In the Service Description field, type Login and logout service
- In the Service URL field, Enter the following URL:
:8080/emapp/EMAppServlet?device=#DEVICENAME# Select System > Enterprise Parameters Under Phone URL parameters, change all fields from CCMNAME :8080 to IPADDR :8080. Change ONLY your existing server name to the correct IP address. Click Save Click Ok from the pop-up warning. Click Reset In the pop-up window select Reset Click Close Select Device > Device Settings > Default Device Profile From the drop down list, select the phone model to be configured, for example, Cisco 7960. Under Description, enter a description of this profile. Under Phone Button Template, select Standard 7960 SCCP. Click Save Repeat for each model phone to be configured Choose Device > Device Settings > Device Profile and click Add New. From the drop down list, select the phone model to be configured, for example, Cisco 7960 Click Next Enter a Device Profile Name, for example “Your Name” . From the Phone Button Template field, select Standard 7960 SCCP. Click Save. On the left hand side of the screen, click the link Line  – Add a new DN. Choose a valid DN from your internal dialing plan for the location, enter that DN in the Directory Number field. Under Route Partition, select your city’s Headquarters Partition. Under Directory Number Settings choose a CSS of appropriate access. Enter any Call Forward and Call Pickup Settings as necessary. In the Display (Internal Caller ID), enter the User’s name. Click Save. From the Related Links: menu, select Subscribe/Unsubscribe Services. In the Select a Service, select Extension Mobility, then click Next. Click Subscribe. Click Save. Repeat for any additional lines. From the menu, select User Management > End User. Click Find Select the user from the list that matches the profile that was created. Under Extension Mobility > Available Profiles, select the profile and move it to the Controlled Profiles selection. Under Default Profile, select the profile. Click Save. Select Device > Phone from the menu. Select the phone from the list of devices. In the Related Links: field, select Subscribe/Unsubscribe Services and click Go In the pop-up window, under Service Information, in the Select a Service pull down menu, select Extension Mobility. Click Next Click Subscribe Click Save Close the pop-up window. Under Extension Information, check the Enable Extension Mobility box. Under the Logout Profile field, select – Use Current Device Settings – Click Save. Click Ok from the pop-up warning. Click Reset In the pop-up window select Reset. Click Close.