If you're following the Cisco v. Apple drama you'll be interested in this. As reported in Ed Burnette's excellent Software, gadgets and games blog Cisco may have lost the iPhone trademark when it was apparently abandoned in late 2005/early 2006 because they weren't using it.
According to Jay Behmke, a partner at CMPR who specializes in trademark law,
The Cisco iPhone trademark was registered 11/16/1999 (Reg. No. 2293011). In order to keep a trademark registration active, you have to file a Declaration of Use on or before the sixth anniversary of the registration date, in which you state, under penalty of perjury, that you have been using the trademark continuously during that period. The sixth anniversary would have been 11/16/2005.
Read more at Burnette's blog.