The truth is it depends on how technical of a person you are. Online organization may help you. It may not. The option of doing all paperless online type of management is much more expensive than buying a notebook to carry around with you. Online organization does exist though. With my company we have a Microsoft Exchange server and have experimented with a few contact managers and so on.
Right now I have my appointments, contacts, and task list set in my cell phone. Which syncs over the Internet with our server constently. That server also syncs with my Laptop, my desktop at the office, and my home computer. When I enter a new contact or appointment on any of the devices it syncs with the server and then all my devices sync with it. If everything is on and conected it takes usually less then a minute, but sometimes up to 3. If I am in an are where my cell phone doesn't work and I don't have my laptop, I can go to a web site and check everything as well. Now everyone in my office has a similar set up on the server and we can invite attends to appointments or share contacts and so on. My secretary in the office can put a tentative appointment into the server for me and it updates on my phone. It askes if I would like to attend. I can send back yes, no, tentative or reschedule, a whole number of options. The best part of it all is that my phone reminds me of when I have an appointment in 15 mins (which that setting can be changed too).
If you are looking for something like that, it is great. Usually bigger companies have an infrastructure set up like this. If you are an individual it may not be cost effective.
The best way is to find a company that will host and maintain the server for you and then you just set up your devices. Pretty much any computer will work, but not all cell phones are compatible. You need either a windows mobile phone, a treo, a black barry device or an iPhone. These types of phones have note taking options as well. Windows Mobile actually comes with a mobile version of office including word, excel, onenote and powerpoint. You can sync as many devices to an account you want. Most companies that host the way I am talking about charge per account, not per device or anything like that. I think we pay $12.95 a month per account (we use Hasbrooke Internet Services) we have 5 active acounts right now for 5 people. If you have a big number of accounts they will bill you a lot diffrent. Then you need to have a data package with your phone carrier. I highly reccomend an unlimited data package. That cost between $40-$70 a month on your phone bill depending on a lot of factors.
That sounds like it will get you started, there are a lot of online options for sales, and other things that you can add on later as you start to go more towards a paperless and more tech based process.
Oh one other thing we did and depending on how your business is structured it may help you. We use vonage for our main phones in the office. (there are a lot of other companies that do this too not just vonage). But before we had a main office or a secretary. We had a vonage line. We had it set up so that when someone left a message on the office line, It email us through the exchnge server (so it went to my cell phone, if my laptop was on it, and my home computer). We knew someone had called, vonage had an option too that attached a sound file to the email of the message. That ment no matter where we were, I got that email in roughfully 2-3 mins listen to it and was able to return a phone call if needed. Even though I was out shopping with my kids, or was in business meeting 3 states away. My company could have a quick, educated, and desicive responce.
Hope that helps you decide if you want to go that route or not. Sometimes a notebook is just as good of an option. It really depends on what type of person you are and what you are doing. If you have any questions I'll be happy to post back more thoughts, because it has really worked for us. I was the same way with notes everywhere, some got washed or lost by other means. I never seem to have the one I needed with me when I needed it. Now it is all fixed through setups like what I discribed.
Good Luck