Corporate World....Lend me your ears!

My biggest difficulty is getting access to people who are willing to listen and give you a chance to share your product or service in the "BIG Corporate World". Calls are not returned, SMSes and e-mails are not replied and getting a face to face appointment is next to impossible. In my industry is is unacceptable if a call is left unanswered or a person left waiting without a response as we are governed by a code of ethics.
1. Is this common culture when it comes to presenting your service to large corporations i.e staff >50?
2. How do i get my elevator pitch converted to a response (positive or negative...just give me a reply)?
3. Being heard by corporate agencies is tough enough, How do we get noticed by Government bodies and their agencies?