Okay, so maybe people will stop bugging me about this. I can tell you I've gotten at least 3 dozen emails and countless comments on this topic. Finally, the American Nokia Configurator supports the Nokia 6600. If you need network settings for the 6600 go there, walk through the wizard and it'll send you an SMS configuration message with the proper settings for data access over GPRS.
I just used it to grab the settings for AT&T Wireless for both MMS and "Browser" (used to be WAP - they still have *no* idea what to call that functionality). I just checked and there's settings info for T-Mobile as well. If you're using Cingular, you're out of luck with the configurator. You'll need to go here for Cingular settings.
Hope that helps.