Absolutely this. A single digit system is great for learning the concept and the basic formula for memorizing. It is massively limiting for everything else.
You could. But really, at that point, all you’re gaining is a LITTLE bit of variety to your mnemonic elements. You’re not improving your efficiency, you’re just delaying moving on to a stronger more longer-term solution.
In spite of this, I’d highly recommend you look at 2-digit systems. My personal preference is to use the Major system. It’s worth putting in a bit of effort to learn the sound associations (there are only 17 total sounds, mapped to just 10 numbers.) With some consistent practice and good examples to learn from, you should be able to start using it within a week or two. Once learned, you really can just “read” numbers directly like words. If the words you associate with your numbers are nouns, it becomes second nature to start seeing the numbers as those images just like seeing the word “dish” or “mouse” can cause an image of that thing to effortlessly spring to mind.
The other huge benefit from upgrading to a 2-digit system like Major is that you double your efficiency for data compression. Right now you have to intentionally evaluate, translate, visualize, and encode each digit into a representative mnemonic element. It’s a 1:1 digit-to-element compression ratio, not very efficient. A 2-digit system provides a 2:1 compression ratio. Double the digit storage per element, allowing you to encode in twice the speed, and only need to recall half the images compared to your current single-digit structure.
A 10 digit phone number currently requires you to use 10 elements to encode and visualize in the correct order, whether through a story, linking, or whatever. So like 860-555-0119 needs something like “a Snowman swings a Golf Club and hits an Egg that land in a Wheelchair which smashes into two more Wheelchairs, which rolls over another giant Egg, splattering a Candle which tips over and lights another Candle on fire, which lights the ear of an Elephant on fire.” Building scenes like this is a LOT of work to encode 10 digits.
Compare this to using the Major System where this same phone number would be encoded with something like “a FiSH slaps a SeaL, who spits out a LoLLy, that lands in a car SeaT that is attached to the car with tons of TaPe.” Those 5 key elements represent all 10 digits.
Here’s a really good rundown of the Major System that may help you get past the difficulty you had with it in the past.
And here’s an example of the kinds of words that can be used to fill in People, Objects, and even Actions and Adjectives using the system. (For now, just try to find a single good match for each number, a Person or an Object, so that its very easy to visualize.) It’s best to try to come up with your own words to associate with each number, simply because if your own brain comes up with it, you’ll have the advantage of some kind of connection already being present. If you have to force associations from someone else’s list, it can take longer to burn them in. That said, feel free to pull from that list or use a resource like memcoder.com to help if you get stuck trying to find fits for some numbers.
It may seem like a big undertaking to pre-define and learn 100 new associations but in the grand scheme of things, this one-time upfront cost will bring a huge return on investment. If you use a flashcard program and work on learning them for about a half hour or so each day, sets of 10 or 20 per day, you’ll have them pretty solid within a month.
Down the road, you can expand the system to include a person and an object for each number (both following the system structure) to provide even more variety to your scenes. You can even add actions and adjectives to spice things up further, turning 6 or 8 digit sequences into sentences that can be read into visually unique single scenes.
One final benefit I’ll mention to learning a 2-digit system is that if you have any desire to try memorizing playing cards, you can easily map all 52 cards on to your numbers and give you a two-birds-with-one-stone system.