Google Voice is using this number as CID for GV calls routed to IPKALL virtual/voip phone numbers in the 206/253/360/425 area codes. The reason for this is to get around IPKALL's call termination fees.
If you are a GV user pointing to an IPKALL number, you will see this instead of your GV number. If you call other people who use IPKALL, they will see that number as well. I do not know if *all* called numbers in those area codes will see that or not.
This could be the beginning of the end for totally free phone calling to/from our PC, since IPKALL makes its money from termination fees. If GV gets around paying them, IPK can't afford to keep giving out free numbers.