According to a very interesting article by Ed Burnette over at ZDNet, it appears that Cisco might have lost their rights to the iPhone trademark for failure to file the necessary materials that prove usage of the term iPhone within the prescribed time frame allowed by the USPTO.

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. Cisco would have had to filed this by November 16, 2005. If they would have paid an additional fee, this could have been extended 6 months to May 16th, 2006. They filed a declaration of use on May 4th, 2006. Part of the requirement to keep the trademark active is to include a copy of the label or packaging that shows the trademark in use. Cisco filed a photo of a Linksys CIT200 Cordless Internet Telephony Kit, with a sticker showing the word "iPhone