It's important that you are both persistent and patient when dealing with people in this business. Before I first signed on with my current publisher, I mailed several different songs over several months before I was finally offered a licensing deal. After I mailed the first song I eventually licensed to my publisher, I waited for close to six weeks and heard nothing back.
On a whim I sent a follow up email and received a response back almost immediately that she was interested in the song but didn't think she had an immediate need for it and that she would consider accepting it into her catalog. I replied back that I completely understood and that when she was ready I would be happy to work with her. She ended up sending me all the paperwork the very next day.
I'm telling you this story because I think it's important to realize that people working in this business are often times very busy. You can't assume that because you're not getting an immediate response that it's an indication that they don't like your music. It might be, but you don't know. It's always best to be proactive and follow up. Don't be annoying, but follow up after a reasonable length of time if you don't hear back from someone. Sometimes they just need to be reminded of who you are and what you have to offer.I personally prefer emailing first as opposed to calling.
I find it less obtrusive and I've found that many professionals in this business will gladly email you back and many will welcome your submissions. Use your discretion, if you're not getting a response feel free to pick up the phone and make contact that way. Just make sure you use common sense and avoid harassing people