Using index cards might help
I am still a newbie and am just implementing GTD, but I think that something that I am doing might be helpful for you.
Disclaimer: The process below only describes what I am doing right now, I can't say if it will be my "final" system. Rather, I am doing it for now as I don't want to commit to anything one system just yet. I think that this hesitancy comes in part from my having struggled on and off for 10 years to get the hang of my Franklin Planner--which I am so happy to be rid of! But, I digress...
I like the immediacy of pen and paper, particularly because I don't have to turn pen/paper "on" and switch to the appropriate program before I can capture my thoughts. So, I did an initial "brain dump" on a flip-chart easel with post-it backed pages as this gives me a LOT of room, and allows me to feel totally unconstrained and like I have a "lot of room to think" without running out of space.
Then, after the brain dump, I put each new idea on a separate 3" x 5" index card. This made it really easy for me to file things according to Context. It also has the side benefit of being a nice detour around the need that I sometimes have to re-write a list with too many cross-outs on it.
I then made separate File Folders for each Context, and sorted each of the index cards appropriately. In some cases, a piece of paper from my "real" inbox triggers a Next Action, and it has sufficient info on it in order for me to DO the NA, I put the paper itself into the appropriate folder. In this way, it can serve as it's own reminder and I don't always need an index card.
What's better, if the support material isn't "precious" and I can write notes directly on it (i.e. if I left a message for the person I can note the date and time of my call). But, if the paper is "precious" I just do all the writing on an index card and then paper clip or staple the two items together.That way, the paper moves from the appropriate context folders in an easy way, and when I am in that Context again and "looking for some action" to do, I have everything I need to "just do it."
This can work really well when you are waiting for someone to call you back after leaving them a voice mail--just grab your "Waiting for" folder and everything you need is at your fingertips.
As an aside, I have found that the best place for my Errands folder is WITH me. Which means, generally, that the best place for it is in my car. I typed up a list of staple groceries and put a photocopy of it in the Errands folder.
Today, though, I was with a friend, and she was driving, and on the way back she wanted to stop by the drugstore... Of course, my Errands list was in MY car, not hers. So, I have realized that Iwould probably do well to shrink down that entire folder to just the size of the index cards--that way it can be a Hipster PDA that I can carry in my purse.
Anyway, BACK to the phone thing--you can also use phone message pads for phone calls to note the time you call someone if you don't like the idea of index cards. They are also helpful when you get a voicemail and need to return their call--just record the info as usual on the slip, and put it into your Calls folder...
Sorry for the long message, but I hope that this helps some!
~Cindy