If I use the search option in People it seems to search on both company name and surname but not phone numbers.
Is there a way to search for a phone number or part of a phone number in People?
There is a third party app doing just that. It's called truedialer and is available to download for free at the marketplace: http://www.windowsphone.com/sv-se/apps/8f10c0bf-541b-47f5-a07e-1bffc785e7c1
I just tried it by writing my brothers 5 last numbers and it showed it right away. Clean and simple :)