XML::Atom::Entry objects don't have a method named im:name. In fact, it's even a valid Perl subroutine name. To get arbitrary XML elements, you need to use get and set.

But first, you need to know the namespace to which the element (name) belongs. It's not "im". That's just an arbitrary identifier. It's the uri to which it is associated that matters. Looking at the feed, we see it's http://itunes.apple.com/rss.

Now that you have the element name and the name of the namespace in which the element belongs, you can use get and set.

my $itunes_ns = XML::Atom::Namespace->new(
   itunes => 'http://itunes.apple.com/rss'
);

my $name = $entry->get($itunes_ns, 'name');
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I used the more meaningful "itunes" over "im". Like I said, the identifier itself is meaningless.