An editor needs to know you can write good dialogue as well as come up with sparkling ideas. As they want to see artists can really draw their characters, so they'll also want to see that writers can really write for their characters. Include a stamped addressed envelope. If you do phone leave it until about four weeks after sending your submission. Plus, be polite and be quick.
Editors are always busy, even on the toilet.
Then leave the envelope unopened in a box file somewhere. The date stamp on the envelope serves as the indicator of when you sent the company your work, so if your character appears in another form you at least have some evidence of your creations being ripped off. Many American companies adopt the same principles as TV companies, requesting that you send a legal release form with any submission so they can avoid any potential legal wrangle if 'simultaneous creation' occurs. The first couple of years you don't make enough to pay the bills. The next couple of years you barely make enough to cover the bills.