I'm going to buy CallManager 7.0 with 2x7816 servers. I wonder what the "seat license" is? If I only buy Device Licenses for IP Phones, can the system works?
You will need to buy node licences, this allows you to run the CM software; one node licence for each CM in your cluster.
then buy an X amount of device units, depending on what devices you want to run and how many.
You can do the calculations by logging onto a CM and go to SYSTEM-->Licence calculator. this will show you the device units required per phone type