Well, that just cuts it down from 2 numbers to 1, and it assumes that the caller ID hasn't been futzed with. Certainly plausible, just perhaps slightly less reliable.
No, it cuts it down from many many numbers (2 numbers per driver/passenger pair) to 1.
I haven't seen an instance of caller ID being 'futzed' with in domestic calls from domestic mobile phone numbers, but I agree it could happen for people roaming internationally.
I haven't seen an instance of caller ID being 'futzed' with in domestic calls from domestic mobile phone numbers, but I agree it could happen for people roaming internationally.