What it is:
Phone encryption model Secure Line ™ 700 is a phone encryption and cellular encryption device that works as a privacy phone for secure communications. It offers telephone encryption for secure communication of office and business phone calls from eavesdroppers trying to listen and monitor them.

Specifically, the SL 700 secures:

Cellular Voice Communications
Single Line Phones
Voice Communications via PBX
Files in any Computer, Network or on the Internet
E-mail Attachments
Point to Point File Transfers (connected to computer)
Compatible with Secure Line™ series of products (SL-800, SL-1400, ULP-1)

Connections & Protections:

The SL 700 connects to ordinary telephone lines, allowing easy encryption of voice communication between other SL 700 units.
The SL 700 provides a simple method of encrypting computer files.
Select, encrypt, and save files through the SL 700 insuring that important information is kept confidential. The encrypted files can be stored in computer networks or on the Internet.
The SL 700 can protect important information contained in computer hardware as well as securing the communication of an e-mail attachment and point to point file transfers.  The user can connect any cell phone through the RS 232 Jack to the SL 700, insuring cryptographic communications of information between other SL 700's.  The SL 700 allows secure, simultaneous voice communication (SVD) and file transfer over ordinary telephone lines.

Development Background:
The SL 700 combines the communication technology of SITG with the Harris corporation's Citadel™ CCX cryptographic chip. The result is a compact and portable security system that ensures e-mail, voice, fax, and data communications are secure. 

Reason for using the SL 700:
Because confidentially isn't a luxury, it is a necessity.