Does the iPhone allow Circuit Switched Data dial-up?
In theory (totally theoretical) the iPhone does support CSD on the tech sheets, but you'd need your network provider to provision it onto your phone, and there's no apps in the app store that would allow you to do it due to the hardware access it'd need. 

You could probably do it, but you'd need some jailbreak software and matching hardware which if you've got an engineering background wouldn't be impossible, but merely a pain in the backside.