I use iPhone. I take notes in the inote. If something happens to my phone everything is backed up in ICloud. I also use a todo app for installs and other work. When Im done i e-mail it to myself with a few clicks. That way when I sit down on my desktop to do billing I have everything.
Also with the inote. I use it as an estimate. I just ask for an email address and send them a copy. By the way my email has a signature that is a disclaimer with all my conditions and warranty. That way they don't comeback at me with bs later.