There's a struggle point for many analog users (pen and paper people to the non-stationery geeks) when it comes to finding a balance between using their paper based system and their smartphones.
What should go where?
Deciding what information is best in what platform is a matter of personal preference. In this case I defer to physics. If there is information that I might need, but can't guarantee will immediately or frequently need, I place it in my digital system (OneNote). If I can guarantee I will need it quickly and in the immediate future, I put it in my analog system (Traveler's Notebook). For example, when traveling my hotel information goes in my phone but the confirmation number also goes into my TN since I know I can turn pages faster than I cas search on my smartphone.
Which do I trust more?
In this case trust isn't a matter of reliability, it's a matter of accessibility. Which system do I trust to accurately capture and provide information back to me? There's no clean cut-and-dry answer here because if I can't trust the tools, they're worse than useless. Paper and pen are pretty easy to trust, but digital systems need greater scrutiny.
Should I use only one?
Now this is a tough one. Should I bite the bullet and put all my information in just one system? For me, this isn't an option on a number of levels but one of the most basic is that I enjoy using both systems. If I can consistently access my information why should I deny myself the benefits and joys of both?
How do I avoid double work?
This is the most common concern. How do I prevent duplicating efforts and losing the benefits of each system through unnecessary effort? My approach is to think about each capture or effort and make sure I know how the information will be used, where and when it will be accessed, and what will be needed at the time. By answering those questions, I can make sure (to a reasonable degree) the right information in going in the right places.
There is no clean rule to using digital vs. analog. There are no directions, manual, or book that will give you the perfect solution. You need accept that taking time to tune and refine your system is critical in it's long term success. If your system isn't growing and improving with time, then neither are you.
Here are some other articles about journals and smartphones you may find of interest: