No doubt, we live in the age of information. Phone calls, email messages, texting, instant messaging, faxes, facebook, etc… They are all the same in most cases - distractions from making true progress in your day. How often do you go home at night thinking that you had a really productive day?
In order to add productivity to my day I turn off my phone. Seriously I turn it off, and that means that I miss a lot of calls - but that's ok. I don't even want to hear it ringing. You need to learn that your day belongs to you, not someone else.
We're in 2012... why would we need to have a phone call when email works so well, and is so efficient? If you aren't willing to turn off the phone, then at the very least, don't answer any calls from numbers that you don't recognize. If the person is not willing to leave you a voicemail, then it wasn't important.
And if you are still running your customer support and need to speak with customers, then you should seriously consider outsourcing it. I really believe that the phone is the single biggest distraction that most of us face in a given day.
I have google talk set up, so that every time the phone rings, I can ignore the call, and then the voicemail goes directly to my email. If it's an important message then it gets left in the inbox so I can deal with it, and if it's not, then I simply delete the email. No more calling into a number and listening to messages on the phone, and having to take notes, etc... Just try this for a few days. It's very liberating.