A lot of the cellular technologies are digital and/or encrypted making transmissions more secure. However, this really isn't where the vulnerability lies. The vulnerability is access (especially physical) to these devices and the servers which facilitate their communications. Log files containing confidential information can be stored forever - who really knows what's happening with them? In addition, there are emerging malicious code threats to wireless devices threatening the security of them. There are new products coming to the market such as those offered by e-Vantage Solutions and others that can help manage enterprise IM to help with these matters. Bottom line, use encryption and anti-virus software if its available for your specific device, make sure your wireless devices have good physical security, and consider not sending anything via IM that you wouldn't want stored forever or the world to see.
This was first published in April 2003