You'll come across this in the recommended documentation, but I'd thought that I would mention that in your example:

my $returnvalue = Common->somesub();
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you likely really want

my $returnvalue = Common::somesub();
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...assuming you want to use modules to package together functions. Common::somesub() is a fully qualified subroutine, Common->somesub() is a class method. Here's a clumsy example of (some of) the differences:

package Foo;
sub bar { print join( ',', @_ ) . "\n"; }

package Baz;
push @ISA => "Foo";

package main;
Foo::bar('arg1');
Foo->bar('arg1');
Baz->bar('arg1');
Bar::bar('arg1');

__END__
arg1
Foo,arg1
Baz,arg1
Undefined subroutine &Bar::bar called at - line 9.
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