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From Theo Lindebaum:
WhatsThatNumber - When you don't know who you are looking for.WhatsThatNumber is a small, fast Contacts Search program that differs from the standard contacts search by including additional fields in the search, and will match on any matching fragment - including telephone numbers, e-mail addresses, related people and the Note field. The contact picture is shown in the results. (This can be turned off if desired).Uses include: - Locate contacts using keywords you have put in the notes field. - Identify received calls, and dialled calls on your telephone bill. Use the last 4 digits for a quick filter. - Find a contact when you are not sure of the correct spelling - typing in a few letters will usually narrow it down to a few contacts - Search Related People names (not included in the standard search before iOS6) - Searches all Contact Groups automatically Once you have located a contact, you can edit, make calls and send messages just like the standard contacts application. You can also add a new contact from this App.iOS 6 does include additional Contacts fields (including notes and related people) in the standard search, but still will not locate number or name fragments in the same way that WhatsThatNumber does, and so it remains a useful addition on iOS 6 devices.On iOS 6 devices, you will need to give access to the Contacts database for the application to work. The first time you launch the program, it will ask your permission. You must allow access if you wish to use this application.