in the uk we have similar situations whereby you register the pc that will be using the broadband (regarding cable modems)
what actually happens is that the mac address of the pc is noted on the router or whatever the company supplies...if the mac address changes then you cant connect.
It is pretty simple to spoof a mac address, and many routers etc provide a facility to enter a "user-defined" mac address.
This is useful for UK chaps as they would register a pc, note the mac address, disconnect the pc, plug in the router, override the router mac address with that of the windows pc, then change the mac of the windows pc to any other number and it all work fine again.
maybe iburst are using a similar scheme.
in which case a similar solution will work.