Have phones 2001,2002,2003 in SRST mode in a router. Calls coming into the system from PSTn should hit 2001 first and then on 2003.
alias 1 6175222001 to 2001 preference 1 cfw 2003 timeou 4 huntstop
alias 2 6175222002 to 2001 preference 1 cfw 2003 timeout 4 huntstop
alias 3 6175222003 to 2001 preference 1 cfw 2003 timeout 4 huntstop
Dialplan pattern doesnt have any effect in the called number when alias is configured. So you have to configure full 10 digits in the alias command. Alias
In addition to supporting message buttons for retrieving personal messages, Cisco SRST allows the automatic forwarding of calls to busy and unanswered numbers to voice-mail systems. Voice-mail systems with BRI or PRI access can log in to the calling phone's mailbox directly. For this to happen, some Cisco CallManager configuration is recommended. If your voice-mail system supports Redirected Dialed Number Identification Service (RDNIS), RDNIS must be included in the outgoing SETUP message to Cisco CallManager to declare the last redirected number and the originally dialed number to and from configured devices and applications.
Step 1 
From any page in Cisco CallManager, click Device and Gateway.
Step 2 From the Find and List Gateways page, click Find.
Step 3 From the Find and List Gateways page, choose a device name.
Step 4 From the Gateway Configuration page, check Redirecting Number IE Delivery – Outgoing.
call-manager-fallback
voicemail 92145425600 —- when somebody hits message button it calls main site's voice mail pilot number
call-forward busy 92145425600 — for calls that are busy, redirect to main site's voice mail pilot number
call-forward noan 92145425600 timeout 15 — for calls that are not answered, redirect to main site's voice mail pilot number.
call-manager-fallback
cor incoming <corlist> <list no> <list of numbers> ### applies corlist to outgoing calls from the IP phone to the router (SRST)
cor outgoing <corlist> <list no> <list of numbers> ### applies corlist to incoming calls to the IP phones from router (SRST)
List number can be from 1-20.
List of numbers should be separated by a dash and space to specify a range of phone extensions.
ex: cor incoming test 1 3001 – 3002
Applies cor list "test" and creates list 1 applied to numbers 3001 to 3002.
Default cor list
call-manager-fallback
cor incoming test default
This command applies cor-list Test to all incoming calls (w.r.t SRST router).
call-manager-fallback
no huntstop
alias 1 9725425979 to 5001
alias 2 9725425979 to 5002
alias 3 9725425979 to 5003
pickup 9725425979
This way when a call comes to 9275425979, it will randomly route calls to one of the three numbers 5001,5002,5003. Using pickup softkey any phone can pick up the call ringning on the phones
alias command also has a preference parameter. This is mostly used if you are entering specific matches rather than wild cards in alias command. For example, if you want to use an alias for IP Phone 4000 to send calls to 5000 if the phone is not registered, then make sure that you give a higher preference in alias as opposed to what is entered in the max-dn command
call-manager-fallback
max-dn 10 dual-line preference 1
alias 1 4000 to 5000 preference 5
Alias and Huntstop
The alias huntstop keyword is relevant only if you have also set the global no huntstop command under call-manager-fallback.
The alias huntstop keyword allows you to turn huntstop behavior back on for an individual alias, if huntstop is turned off globally by the no huntstop command. Setting the huntstop keyword on an individual alias stops hunting at the alias, making the alias the final member of the hunt sequence.
SRST call-forwarding for busy and no answer can be set system wide
call-manager-fallback
call-forward busy <number>
call-forward noan <number> timeout 10
SRST vs CCM Callforwarding
Call-forward-all settings under regular Callmanager mode, is not retained by the phones when they go into SRST mode.
Call forward number transformations
You can also transform the extension number for call forwarding by using wild cards.
call-forward busy 40..
If a user calls 5010 and the user is busy, then the call will be forwarded to 4010.
Call forwarding on individual lines
alias 1 1001 to 1001 preference 1 cfw 2001 timeout 20
In this example, you have created a second dial peer for 1001 to route calls to 1001, but that has preference 1 and call forwarding to 2001. Because the preference on the dial peer created by the alias command is now a lower numeric value than the preference that the dial peer first created, all calls come initially to the dial peer created by the alias command. In that way they are subject to the forward as set by the alias command, instead of any call forwarding that may have been set globally.
This feature can be used to create a basic hunt group setup using Callforwarding logic.
SRST reference has 3 fields (In CM3.3)
IP address, SRST reference name and TCP port which should match with what is configured on the router.
In CM 4.1 two more field were added:
a. SRST Secure – check box. If checked will use SRST in secure mode (encryption)
b. SRST certificate provider port – Default is 2445.
