They both include a 50 user CCME/SRST license and a PVDM32 but the C2821-H-VSEC/K9 ($8,295 list) also includes an AIM-VPN/SSL-2 VPN module which bought separately would cost $2,500. this explains the cost difference over the C2821-VSEC-CCME/K9 which costs $6,395.
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There is no difference in functionality. You can run full CME (or SRST) with either bundle as the licenses are interchangeable - the Q-A below is from the document at the link below and confirms this.
Q. Are there any pricing differences between Cisco Unified Communications Manager Express and Cisco Unified SRST?
A. No. The feature license pricing is the same and interchangeable between Cisco Unified Communications Manager Express and Cisco Unified SRST.
If I can add the follwing may be of help to WO Chong or others.
The main function / limitation is VPN
Cisco 2821 HVSEC Bundle with IOS Advanced IP Services, PVDM2-32, AIM-VPN/SSL-2, 50 User SRST License, 10 User SSL VPN License, 256 MB Flash/512 MB DRAM
Cisco 2811 HVSEC Bundle with IOS Advanced IP Services, PVDM2-16, AIM-VPN/SSL-2, 35 User SRST License, 10 User SSL VPN License, 256 MB Flash/512 MB DRAM
Cisco 2801 HVSEC Bundle with IOS Advanced IP Services, PVDM2-8, AIM-VPN/SSL-2, 25 User SRST License, 10 User SSL VPN License, 128 MB Flash/384 MB DRAM
2801 Voice Security Bundle, PVDM2-8, Adv IP Serv, 64F/256D
2801 VSEC Bundle with PVDM2-8, FL-CCME-24, Adv IP Serv, 128F/256D
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