You need advanced ip services or advanced enterprise services feature set. You are running SP services right now.
Also setting up that command, only encrypts RTP payload. You will need to setup Crypto ipsec tunnels to publisher and subscriber to ensure that MGCP signalling is also encrypted.
HTH
Sankar
PS: please remember to rate posts!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus