Hi Roberto,
There is no cost (free) to migrate to CSL Licenses
Migrating to CSL Licenses
When you upgrade to version 7.1 or later, you must replace your pre-CSL licenses with CSL licenses. You are required to migrate your licenses for mailbox features and port features. If you purchased the optional IVR features, you must also migrate your licenses for the IVR features. The migration procedure for each of these types of licenses are described in a separate section below.
Note 
If you are upgrading to the same of licensed features as before, the CSL licenses are free.
When you obtain licenses for features for Cisco Unity Express 7.1 or later, the licenses are available only in the increments shown below. The following types of licenses are available:
•Mailboxes (available only in increments of five)
•Ports (available only in increments of two)
•IVR (available only in increments of two)
Note CSL licenses are the same for all supported devices. See the Release Notes for Cisco Unity Express for a list of supported devices.
The corresponding SKUs for these licenses are:
•FL-CUE-MBX-5
•FL-CUE-PORT-2
•FL-CUE-IVR-2
•FL-TCV-USER-1
To migrate to CSL licenses, use the following procedure:
1. Use the show software license command to determine which pre-CSL licenses you have.
The name of the pre-CSL licenses include the incremental quantity of the license. For example SCUE-LIC-25CME.
2. For mailboxes, add the number of GDMs (Group Delivery Mailboxes) that you will be using because they were not included in the pre-CSL counts but are now being represented in the CSL counts.
3. Divide the total number of pre-CSL licensed features by the incremental quantity represented in the name of the appropriate CSL SKU.
For mailboxes, divide by five. For ports, divide by two. For IVR sessions, divide by two.
If the result is not a whole number, round up. This will give you the explicit quantity of CSL incremental licenses that you need.
As an example, if you have the following pre-CSL licenses and you have 10 GDMs:
•SCUE-LIC-100CCM
•8 instances of SCUE-LIC-PORT-2
•SCUE-IVR-S16
You will need to choose:
•22 instances of FL-CUE-MBX-5
•8 instances of FL-CUE-PORT-2
•8 instances of FL-CUE-IVR-2
Using the Migration Portal
Note You must have a Cisco.com password to access some of the URLs in the following procedure.
Follow these steps to obtain a migration license for your existing Cisco Unity Express 7.1 features:
Step 1 Go to the licensing portal at www.cisco.com/go/license and click the link at the bottom of the page to go to the license migration portal.
Step 2 On the router that is running the features that you want to migrate, enter the show inventory command to see the corresponding product IDs and serial numbers.
Step 3 Enter the appropriate product ID and the serial number and click Continue.
The product ID is the type of Network Module that you are using, such as AIM-CUE.
Step 4 Use the drop-down menus to select the product family, product, and feature (SKU), then click Continue.
For the product, use the SKU that you determined in the previous section for the features that you want to migrate.
Enter your registration information, including your company's name and e-mail address, then click Continue.
Step 5 Verify all of your license information and click Submit to receive the free CSL upgrade license file by e-mail.
Step 6 Repeat the appropriate steps above for each device that is running features that you want to migrate.
Step 7 Copy the license file(s) to a FTP or TFTP server.
From this good doc;
http://www.cisco.com/en/US/docs/voice_ip_comm/unity_exp/rel7_1/Licensing/Using_CSL.html#wp1102792
Cheers!
Rob
