>  There is an algorithm for using 7 of the digits, but for the life of me I cant find it or even remember what it's called. I thought it was being used in Contacts... 

I think you're thinking of the SimplePhoneMatcher used in the dialer

> I think we can look at the last 8 digits of any number for safe comparison

And what happens when the number has spaces/etc ? We should probably use SimplePhoneMatcher after all, this is a good idea, even if this is yet another way to match...