From my own experience, you usually get most of your enterprise clients among companies people you've worked with in a way or another, and people you already know from elsewhere. Basically this is networking, networking, networking and networking again. So yes, actually LinkedIn counts. It may even counts a whole lot.
Cold phoning may work, but it's extremely tough and unrewarding because you have to get prepared to call 2000 times, get screamed at 100 times, ignored 1800 times, find interested people 100 times, and get finally 5 meetings, of which you'll maybe obtain 1 or 2 customers in the end. So you really want to have the nerves to go over that, not everybody does, especially not the nerd programmer type :)
AdWords may work. However in the past few years it quickly degraded from a sure way to get customers when spending 500-1000 euros/month to something you need to carefully attend for to get some bang for the buck. Be prepared to study your keywords and statistics, make many tries and spend some money on it before getting results.
Speaking of it, website quality and landing pages are of absolutely tremendous importance to web ad conversion. Don't ever forget that.