From: ahk@chinet.com   
      
   Stephen Sprunk  wrote:   
   >On 22-Jun-14 13:14, Adam H. Kerman wrote:   
   >>Jishnu Mukerji  wrote:   
   >>>On 6/21/2014 11:33 PM, hancock4@bbs.cpcn.com wrote:   
      
   >>>>I have no idea what the voltage/currents are on VOIP phone   
   >>>>lines.   
      
   >>>On my VOIP phone line which is an optical fiber, both voltage and   
   >>>current are zero as far as I can tell :P   
      
   >>>Oh you meant from the modem to the phone? My old POTS phone from   
   >>>AT&T still works so ..... :)   
      
   >>That's hardly the test. Try using a 28.8k modem and let us know if   
   >>you can get it to synch with another modem.   
      
   >Most VoIP gateway vendors recommend getting a real POTS line if you   
   >intend to use modems or fax machines.   
      
   They're not always available, so they shouldn't be creating situations   
   in which it's impossible to use ordinary communications equipment.   
      
   >AFAIK, there is no standard like T.38 for modems.   
      
   That's because the phone company never wanted to guarantee quality of   
   analog voice lines and the manufacturers couldn't impose any standard   
   on the phone company. Nevertheless, the range of conditions within which   
   modems would work is known.   
      
   >Why would you want to use a modem over a VoIP line anyway?   
      
   The point would be that it's a true test of whether the analog side   
   is making any effort to supply a quality voice line. Also, sometimes a   
   pair of modems is the best solution for communication.   
      
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