Where you convince someone to go away with a valid reasoning (when you might be able to help them)
Usually used to save both parties time
Technical support company's might suggest a client goes to their ISP if they have internet issues to troubleshoot 1st with them, 90% of the time the issue is with the ISP however the techs could have checked a few things prior to confirm this is the case.
If something can be done but its not feasable (ie would cost millions to develop a system to do x y or z for something that's never gonna make money) advising person with request not possible is a Le Fobb
Fault is External. Typically this is commonly used regarding technology, where someone thinks their device is faulty and when asking someone who is knowledgeable of the device they discover the fault is with the user not the device
Your phone issue was FIE, but if you use it the way I descirbed it should be fine from now on