You can pretty much determine exactly how you were called

use strict;
use warnings;

{
  package foo;
  
  use UNIVERSAL qw(isa);

  sub new { bless {}, shift }

  sub callme {
    my $invoker = (@_ == 2 ? shift : '');
    my $package = [caller]->[0];
    
    if(ref $invoker and isa($invoker, __PACKAGE__)) {
      if($package ne __PACKAGE__) {
        print 'called: $obj->method(@args)', $/;
      } else {
        print 'called: method($obj, @args)', $/;
      }
    } elsif($invoker eq __PACKAGE__) {
      if($package ne __PACKAGE__) {
        print 'called: foo->method(@args)', $/;
      } else {
        print 'called: method("foo", @args)', $/;
      }
    } elsif($invoker eq '') {
      if($package ne __PACKAGE__) {
        print 'called: foo::method(@args)', $/;
      } else {
        print 'called: method(@args)', $/;
      }
    }
  }
}

my $o   = foo->new;
my $arg = 'a string';

$o->callme($arg);
foo->callme($arg);
foo::callme($arg);

callme $o $arg;      # same as $o->callme($arg);
# callme 'foo' $arg; # syntax error

{
  package foo;
  callme($o, $arg);
  callme('foo', $arg);
  callme($arg);
}

__output__

called: $obj->method(@args)
called: foo->method(@args)
called: foo::method(@args)
called: $obj->method(@args)
called: method($obj, @args)
called: method("foo", @args)
called: method(@args)
[download]

Of course this is assuming you know how many arguments you're expecting in your method, but it shouldn't be too hard to get around that.
HTH

_________
broquaint