The Computer Interface to Message Distribution is a protocol allowing computers to communicate with messaging platforms such as SMSC's and USSD Centers. It is a low-level proprietary protocol primarily used by devices created by Nokia such as the Nokia Artus messaging centers, and is similar in intent and function to the SMPP protocol promoted by the SMS Forum (which most other manufacturers of messaging platforms use instead). The spec states that it is able to run on top TCP/IP, X.25, or over serial ports.
The specifications, however, are available for download free of charge from Nokia's website at http://www.forum.nokia.com/main/1,35452,1_2_9,00.html (however, you need to get a free registration first), and it appears that there are no restrictions on the implementation and use of the protocol.