Re: Flashing the former firmware image:
It is a known issue, that after you flashed the latest PR image to the phone, the GSM and 3G functionality is lost until you really put in some extra effort(tweaks). These are not trivial, i never needed it, but you might search the forum for it.
Please follow these instructions http://wiki.maemo.org/Updating_the_tablet_firmware Read them carefully regarding your PC OS, because there are some limitations, which, i think, will not be tackled by Nokia ever, to some Win7 versions.
Best result here was and is the use of a Debian- or Ubuntu-based Live-CD or installed system. But mileage may vary, according to everyone's experience and expectations.