UC500.com Cisco CallManager Express, UC500 reference

What is Extension Mobility?

Very simply Extension mobility allows users to have temporary access to other physical phones connected to CME and have all of their personal settings such as lines(directory numbers), speed dials and XML services as if they were sitting at their own desk.  Extension mobility is also used in desk "hoteling" environments where during the course of a day multiple people may use a phone.  An example could be a 24x7 call center where 3 users each with and 8 hour shift use the same desk.

Extension Mobility on CME Concepts.

First supported on CME4.2 
Every phone using extension mobility has to have a logout profile.
Phones must be enabled to use extension mobility.
A User login profile is configured to allow users to login to phones.
Can optionally support up to 50 Agents using Cisco Unified Call Center Express.
IP Phones must have a screen.
Not supported for SIP phones.

Configuring a Logout profile on CallManager Express

All the directory numbers must be configured before attempting these steps.

enable 
configure terminal
voice logout-profile tag  (You may have as many logout profiles as phones supported by the hardware)
username username password password (this is creted for this device when logg
number number type type
speed-dial speed-tag number [label label] [blf] 
pin pin (optional used for call blocking)
end

Example Logout profile

CMERouter(config)# voice logout-profile 1 
CMERouter(config-logout-profile)# user phone1 password 12345
CMERouter(config-logout-profile)# number 4000 type feature-ring
CMERouter(config-logout-profile)# speed-dial 1 6002

Enabling a Phone to use Extension Mobility in CallManager Express

Basically, all you need to do is assign the logout profile to the ephone itself .

Using the logout-profile profile-tag where the profile tag is the tag number assigned to the logout profile you previously created

An Example Ephone Configuration
ephone 2
mac-address 0000.D111.B432
type 7970
logout-profile 1

Configure a User Profile

 This is all the configuration that a user will have when they login to a phone using extension mobiltity.  ephone-dn and ephone templates may be used.

Configuration steps follow

enable 
configure terminal 
voice user-profile profile-tag
name username password password 
number number type type
speed-dial speed-tag number [label label] [blf] 

CMERouter(config)# voice user-profile 2 
CMERouter(config-user-profile)# name user1 password 12345
CMERouter(config-user-profile)# number 5000 type feature-ring
CMERouter(config-user-profile)# speed-dial 1 6002

Sources  - Cisco Unified Communications Manager Express System Administrator Guide