[jft]

I would suppose access to the net through amazon's proxy (use of the browser) is restricted by amazon if you haven't registered the kindle properly. See the other posts about the http header that is send to amazon. There is an id included so amazon can identify the user. So a not with amazon registered kindle means no access to the amazon proxy.

You could only change your kindle id to a valid registered one. But that would mean access to the user account associated with that kindle id.

The other solution would be to disable the proxy. And that's something I cannot approve and will render your included sim card useless in no time (kindle abuse). At least I think it will.