GTD was developed before the age of smartphones and GTA software was not in David Allen’s mind when he developed the system which means that there are plenty of ways that software can improve GTD and make the system even more efficient.
Before smartphone, I carried around a notepad for years and one of the things that I realize that a smartphone can do that a notebook couldn’t is automate various things.
One of the things that is already automatic if you do GTD with a smartphone is our someday maybe list.
If it has a due time, it is not a Someday item. If it does not have a due date then it IS a Someday Maybe item or already correctly filed in your inbox.
If you are taking time to carefully consider a detailed someday maybe list , I say that you are waisting a TON of time when all you need to do to get to someday items is filter for items without a due time.
AND there are MANY MANY MANY other ways that smartphones can save our time.