I'm migrating a lot of phone from CUCM 9 to CUCM 12.5 and I'm working in combine with two options: The first one is configuring a Phone Template under Bulk Administration where this template will have common options to many phone with the same model. Example I can configure a phone template with a Device Pool, Softkey Template, Common Device Configuration, Extension Mobility Option, Partion, CSS, Forward calls, etc and all this could be apply to SIP PHONE 7841 or any other model.
And the Second option that I use in combine with the first one is BAT that is a Excel exported from CUCM where you can modify with the option you need.... In my case I modify it with the fields that I didn't configure in my Phone Template . Example Here I configure the Mac Address of all my phone that have the same model and also here I specify my owner user ID, phone description, Directory Number, Alerting Name, Display Name, etc...
After BAT is completed I save it like txt file and I upload to CUCM and after that I combine the two options to finally create the phones. And I repeat these steps to every phone model....
Also you can do all the configuration using BAT but in my opinion is harder....
