But if you say you purchased it why would you want to put an ISP firmware on it?
I know I would not.
If there is a firmware update and they won't let you have it I would send the device back for a refund.
Try giving them an expensive phone call:
United Kingdom 0906 3022114
(0,50 £/min)This may be cheaper:
saynoto0870.com - 020 7309 0226I phoned them on 020 7309 0226 never realy got anywhere but they said send an Email to them asking why they have this policy for end users.
As I said before if you can't update send it back.