Your marketing should start with your Value Statement. What Value do you bring to your Customers? It's not the technology or your people. Noodle on that for a while.
Next is your website. VZ is halting yellow page distribution because no one uses the YP. So if you ain't on the web with a current website, you will lose out.
What does that website need? Easy navigation. A phone number on every page. A headline above the fold. A call to action on every page.
Instant chat works wonders for lead gen.
Have an about page for your services, like this one: How VoIP Works (just leave out all the words about cheap calls).
You might want to contract a PR firm to pump out the occasional press release - an SEO optimized release.
Testimonials, case studies, a blog and a social media effort are all additional marketing efforts. But you need the basics. Why? Marketing builds Trust, which is required to make sales. Plus cold calling and door knocking are meeting more and more hurdles, so inbound sales leads and referrals become significant lead generation for your business.