Need to look up a phone number that's appeared on your Windows Phone caller ID? Truecaller is a Windows Phone 7 app that will let you not only search by keyword but also by phone numbers.
Results are returned listing the name and address (if available), a link to show the location on TrueCaller's map, a link to search the result through Bing, as well as the ability to call the number or add it to a spam listing. While I like the ability to add a number to a spam list, there doesn't appear to be any way to manage such a list.
TrueCaller also gives you access to International numbers. Just tap the Choose Country at the bottom of the main page and select the Country you would like to search. For the most part, TrueCaller ran smoothly but from time to time, the app crashed while conducting the search. It's not enough to drive you crazy and hopefully the next update will fix things.
There isn't a trial version available for TrueCaller but the full version is only $.99. If you need to search phone numbers, TrueCaller is worth a look at.
You can find the Windows Phone 7 app here (opens your Zune desktop) at the Marketplace and follow the break to see a video of TrueCaller in action.