I've got a pair of these Gandalf DOV 640's (Data Over Voice units) and I was wondering... 1) Is there a difference between 'master' and 'slave' units? I have a pair of what is marked 'slave' units. 2) Does anyone have a manual for these or can anyone tell me what the RDL and TL switches do, along with the dip switches inside? I'm not sure this things strictly meet the 10-year rule, but they should at least be close to it. Thanks for any info! -- Pat