Call signalling traffic goes from phone to CCM server but RTP traffic goes directly between IP phones so the "spoke" sites on your network need to be able to send traffic to each other.
The document at the link below discusses configuring Dynamic Multipoint VPNs to support Cisco voice traffic and may be of use.
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/VoSDMVPN.html
One alternative to using VPNs which may be suitable for home workers would be to use Cisco Phone Proxy.
This allows IP phones at remote sites to connect via to a CCM cluster over the Internet using the built in TLS/SRTP to encrypt media and signalling. An ASA is required at the central site to act as the phone proxy. More details here.
http://www.cisco.com/en/US/solutions/collateral/ns340/ns394/ns165/ns391/at_a_glance_C45-500231_v1.pdf
I was excited when I found out about this feature but upon further investigation was a bit disappointed as IP phone services and directories were not supported (not sure whether this has changed recently).
Please rate if helpful.
