As requested by PM
Please note that I am not a security professional so I can only give you some pointers.
Phase 1 - What email system do you have in mind? Pop3? Exchange? Gmail? You need to look into PGP, and public/private keypairs
Need to know more before commenting.
Phase 2 and 3 can be supported using a secure VPN.
Basically you set up a OpenVPN VPN server at a secure site, and have your clients connect to this server.
You can then use open source, easily available software like Ventrilo to do audio conferencing over the VPN network.
At this point am not familiar with point to point video conferencing solutions. Legacy stuff like NetMeeting will work perfectly though.
As long as traffic stays on the VPN, your data will be protected.
VPN access keys need to be securely transmitted, preferably by CD using registered post. The CD should be destroyed after the key has been retrieved.
Your safety is at the network transport layer in this case. As long as your VPN is not breached, it should be secure.
Client terminals should have full disk encryption to prevent loss of the key or unauthorised access.
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For storage or full system encryption, check out TrueCrypt. This software is great for encrypting attachments and documents.
TrueCrypt - Free Open-Source On-The-Fly Disk Encryption Software for Windows Vista/XP, Mac OS X and Linux
DF