Since the guide (and therefore the warning) are copyrighted, I can't put the exact contents here...  The warning states that only 26 AWG or better phone cables must be used with the system in order to reduce the risk of fire...

This of course begs the question of "Exactly how much current does Lenovo try and put through a phone cable?" and "Does the phone company know they're doing this?"  Are there really cheap aftermarket phone cables out there that can't handle the tiny current that the phone system has?  Are houses burning down all over the world due to this?  Be afraid, be VERY afraid...