I tried to backtrace a phone number to an address book entry today and ended up with more Contacts hits than I expected. Some of the hits did not have the search string in any visible field either.
After some digging around I found out that the spurious matches contain the number sequence I searched for in the UID field. Unless maybe you are a developer, this seems to make not much sense.
Also, the numbers in my contacts entries sometimes comprise extra characters like whitespace, + or - signs. If a contact has number +1 234 4567-890 I will not find it with search strings 234567 or 4567890.
I suppose I could remove all such characters in all entries and search for a clean number sequence next time. However, is there any way to perform a good telephone number search without reformatting the contacts into a much less readable format?