Hello Matthew-
The license consumption will be 100% based on your AAA rules and the features that are being referenced in them.
For instance, if the mobile devices are doing PEAP with AD Username and Password or Web Authentication through ISE's Web Portal then only base licenses will be required/consumed.
On the other hand, if your rules require that mobile devices must be profiled and let's say go through a BYOD on-boarding and provisioning then Base and Plus licenses will be required/consumed.
Here is a link that you can reference on the different ISE licenses:
http://www.cisco.com/c/en/us/td/docs/security/ise/1-2/user_guide/ise_user_guide/ise_man_license.html
I hope this helps!
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