This is what I remember from a few years back. The problems that I've seen come from the softphone, in this case, IP Communicator, binding the wrong IP address. Once the laptop connects to the VPN, it has two IP addresses; one on the physical interface and one on the VPN virtual interface. Now, the bound IP address doesn't interfere with phone registration or call control, but when the voice path is being setup, the CallManager queries each device for the IP address to route the RTP voice packets to and hands that IP address to the opposite end. If that IP address happens to be the physical interface or the users laptop at home, which is most likely a RFC1918 address, the phone in the office will not be able to route the voice packets. And worse, because RTP is connectionless, there will be no error generated.

Therefore, you need to specify the interface/IP address within the softphone to eliminate that problem. I'm afraid that I don't have a copy of IP Communicator, so I cannot walk you through that directly. And, of course, it may be something else entirely.

Good luck.