I succeeded changing amazon's SIM card in my kindle dx graphite to my local GSM provider's sim and getting online
this is what I did:
1. changed sim card in kindle
2. commented these lines in /opt/amazon/ebook/config/browser_prefs
#settings.proxy.hostname = fints-g7g.amazon.com
#settings.proxy.portnumber = 80
#settings.proxy.sslportnumber = 80
btw, if you don't want your kindle to be recognized online as mobile device, change browser identification string in the same file to smt like this:
user_agent.base = Mozilla/4.0 (compatible; Linux 2.6.22)
3. changed DNS server's ip addresses to my GSM provider's in /etc/resolv.d/resolf.conf.3
4. changed some settings in /etc/ppp/chat/connect-3 to be compagtible with my GSM provider's settings (dialing number and AT+CGDCONT connection string)
5. rebooted kindle and thats it! internet worked