How does the 8821 compare to the 7925, 7925-EX, and 7926?
The Cisco 8821 uses the standards-based Session Initiation Protocol (SIP), while the 792x phones use the Cisco proprietary Skinny Client Control Protocol (SCCP) for signaling.
The Cisco 8821(802.11a/b/g/n/ac) also uses standard fast roaming (802.11r, FT) whereas the 792x(802.11a/b/g) phones use proprietary Cisco Centralized Key Management (CCKM) for fast roaming.
The 8821 will also be supported and receive updates for years to come while the 7925, 7925-EX, and 7926 have reached End-of-Life.
Finally it is important to know that the wireless network requirements are different between the 7925-EX and 8821 so a network evaluation should be performed prior to introducing 8821 phones to a network that does not have them already.
*** Important *** The 7925-EX is certified for deployment in potentially explosive environments. The 8821-EX will also be certified for use in potentially explosive environments; however it is not yet available.
What needs to be done on Cisco Unified Communications Manager (CUCM) to migrate from a 792x to an 8821?
The configuration settings on the 792x phones need to be moved over the new Cisco 8821 phone type. This can be done using the Bulk Administration Tool, manually, or using third party migration tools.
Are there accessory differences between the 792x and 8821 phones?
Yes the 8821 phones use a different battery, wall charger, desktop charger, multi charger, and holsters.