[markfenton]

The blackberry facebook app attempts this, but it's not actually that useful. Variations in spellings of names confuse it, the 'type' of number (work, mobile etc.) can cause duplicates and a lot of my friends no longer store any useful contact details on facebook due to privacy concerns.

Some of these might be implementation issues, but I still don't think that even working perfectly it would be a killer feature for a phone.