I wasn’t paying attention yesterday when I opened iTunes it told me there was a new version of iPhone OS that fixed a major vulnerability. Without thinking I went ahead and updated my iPhone OS to 3.0.1 No big deal right? WRONG. All of a sudden XCode no longer recognizes my phone as a development device.
What this means is that I can no longer test code on my phone 
After a quick search I found the solution posted on the iphonedevsdk forums! The original post can be found at http://www.iphonedevsdk.com/forum/iphone-sdk-tools-utilities/21005-xcode-3-1-3-3-0-7a341.html
For those of you who just want the fix and want it now, here it is . . .
(Just paste this line into a terminal window while XCode is closed)
ln -s /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0\ \(7A341\) /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0.1
That did it for me, hopefully it helps you!
[...] Ref1. FIXED: XCode Not recognizing Development Device After 3.0.1 Upgrade [...]
Timely post, appreciated.
And for those of us who are running a 3.1 beta SDK, the corresponding command would be:
ln -sf /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.1\ \(7C116a\) /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0.1
ok, excuse the really stupid question but what is a terminal window?
ok, figured it out, sorry to bother.
`~- I am very thankful to this topic because it really gives useful information `-*