Folks, iPhone 3G shares a common code library with the classic iPhone for v2.0 of the firmware. However, having said that, 5A347 was designed as an internal build to be used only with 3G development iPhone units and does not include several of the code modules required to successfully run on a classic iPhone.
Build 347 is nearly certain to encounter difficulties when installed on a classic iPhone due, in part, to the reasons mentioned above. I am not prepared to say it's dangerous to install 5A347 on a classic iPhone, but it's definitely not a tested or supported firmware version for anything other than development edition 3G iPhones.
Seems to be running on my classic iPhone quit well. And..
If this version wasn't compatible with the classic iPhone you wouldn't be able to install it. I know for sure. You think Apple is really that stupid to allow a firmware designed for the 3G to be installed on the classic?