Oh, where to start.

First off, you have both open FILE and open my $fh. Stick to one style. Specifically the latter. Yes, it's a minor nit normally, but it got promoted to a major nit (if not, at least a lieutenant nit) by virtue of inconsistency. Also, you don't check the first open's return - stick the "or die" in there as well. (Again, a lieutenant nit for the same reason.)

Second, parsing CSV files without Text::CSV_XS. Not a capital crime, but maybe a minor bit of flogging. (Personally, I prefer DBD::CSV, but it uses Text::CSV_XS under the covers, so I save my back from the flogging that way.)

Next, your assignment to all those variables. When I'm doing a massive split like this, I like to use a hash instead of an array. Or individually-named variables:

my @fieldnames = qw(Lname Fname ssn address city state zip phone1 phon
+e2);
my %row;
@row{@fieldnames} = split(/,/, $line); # yeah, I just told you to use 
+Text::CSV, but I'm keeping my suggestions independent.
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You didn't quite show us what you were trying, only alluded to it and gave us context. But the function you're looking for is substr.

my $user = substr($Fname, 0, 1) . substr($Lname, 0, 3) . substr($ssn, 
+-4);
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