John Gruber from Daringfireball asksif members of the developer's program can run other user's apps.
It's a good question, but I think there's an implication in there that's not true right off the bat. I don't think the iPhone will run unsigned apps, period. In the "iPhone OS Programming Guide" it has instructions for obtaining and using a developer certificate, complete with CSR generation and sending that CSR to apple for signing. That gives you a cert that you must build with in Xcode to code-sign your binary.
So it seems like developers should be able exchange source code and test their apps if you build it locally. Can you run other developer's signed apps? Seems like as long as they are signed that should be okay.
But, the kicker on that link is the whole "designate a device for development" and "provisioning profile," which apparently specifies the actions you can perform on that device, "such as whether or not you can make calls." You have to get the profile from Apple, so presumably it's crypto-signed somehow with your cert.
So perhaps the process of designating a device for development then -potentially- (depending on your approval level from Apple) could disable the normal, ATT network access functions (phone and data). That could be a major downer if there's no way to use an app in real world situations without a dedicated developer device.
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