Note on above: there are legitimate reasons for businesses to set Caller ID to something other than the call origin. But the "something other" should be selected from a set under the control of the business, not a free for all. I.e., a desk phone with DID may show as the main company number, etc.
This takes a little more work to account for, but it shouldn't be a roadblock.
No, a phone should give the exact number for that exact phone, since that is whom I want to call back, should I need to. That phone may be manned by more than one individual (in case of shift work), but nobody should have to go through a phone tree.
This takes a little more work to account for, but it shouldn't be a roadblock.