in reply to Trim Phone Numbers

perl -lnpe 's/.*(?=\d{3}-?\d{4}$)/*/'

or another interpretation of your question:

perl -lnpe 's/(\d\d-?)(\d{3}-?)(?=\d{3}-?\d{4}$)/$1=~tr!0-9!*!;$2=~tr!0-9!*!;$1.$2/e 
@_=qw;
Just another Perl hacker,;
;$_=q=print
"@_"= and eval;

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In Section Seekers of Perl Wisdom