You need to contact Cisco Licensing Department and provide them License Count Utility file, they will give you the amount and type of licenses that you must purchase.
After that, you need to provide more migration details, for example, are you migrating from MCS? if so, do you have Unity and CUCM contained in the same IP Address? Are you moving from Virtualized environment?
There are a lot of details that you should take care of before perform the migration.
