Is it possible to search for a contact by phone number in Froyo ? How ?
HTC's Sense UI gives you this functionality out of the box. In the Phone app if you start typing the phone number, it will filter your contacts that include either that number, or the contact's name via T9 representation.
Choose 'Contacts', than 'Keypad' and start entering the phone number.
On my Galaxy S running Froyo 2.2.1 this displays a dropdown box with a number of how many numbers start with the characters entered.