In the "old days" of VOIP there were vitrual phones that were on your PC desktop.
You used a headset for these.
Such an application would be great feature to add value for buyers of your small systems like the UC520.
Accessible only through a VPN these phones would allow the mobile worker to continue to have all the benefits of his/her cisco phone.
For teleworkers I know you want to sell another router and phone but if you want to push down to SMALL business you need this kind of thing if you don't already have it.
Thanks for listening...
The Cisco IP Communicator or CIPC is the soft phone that is supported on the UC520. Please see more details at this link.
Hope that helps,
Customer Support Engineer
Small Business Systems Business Unit