...
By the way, I have a little bit of a story, and I am not sure how much I should tell, but I had a situation in which I needed the seed phrase that was supposed to be in three parts and I was missing one of the parts (for reasons), and so I knew that I had two back ups of the three parts, and so I called up a life-long friend, and he surely is not very technical and even though talked with him about bitcoin several times, his eyes glaze over while he is looking at how complicated his flip phone is or that he is trying to get his remote on his TV to work.. (he doesn't have internet).. but anyhow.. I called him up, and I asked him if he could go to the location in which one of the pieces was located, and I would give him the code to get in, and then I would give him instructions about how to get to it while we were on the phone live, and he said o..k.. and he would call me when he was at the location. It took about 5-10 minutes just to get to locating the place where the words were, and I told him that it would probably be 8 words, and he told me that it is only 4 words.. and then I remembered that it was a 12 word split up instead of a 24 word split.. and so when he read me the 4 words, he mentioned that one of the words was "xxcxxxxx", and I said that does not even sound like a real word, and he read it several times and told me that is what it says. I said o.k... so I wrote down the 4 words, and I told him that I would let him know if I had any problems in terms of getting access to the wallet that I was wanting to get, but I would have to do it in a few hours.
So when I put together all 12 words, and I typed in the "xxcxxxx" by the time I got to the second letter, there was already a suggestion that had the word to be "xxrxxxx".. so my friend could have had sworn that the word the one with the "c" and neither of us even thought about the word with the "r".. so sometimes simple mistakes can be figured out, but some kinds of more complicated mistakes might be a lot more difficult to resolve.
...
By the way, I have a little bit of a story, and I am not sure how much I should tell, but I had a situation in which I needed the seed phrase that was supposed to be in three parts and I was missing one of the parts (for reasons), and so I knew that I had two back ups of the three parts, and so I called up a life-long friend, and he surely is not very technical and even though talked with him about bitcoin several times, his eyes glaze over while he is looking at how complicated his flip phone is or that he is trying to get his remote on his TV to work.. (he doesn't have internet).. but anyhow.. I called him up, and I asked him if he could go to the location in which one of the pieces was located, and I would give him the code to get in, and then I would give him instructions about how to get to it while we were on the phone live, and he said o..k.. and he would call me when he was at the location. It took about 5-10 minutes just to get to locating the place where the words were, and I told him that it would probably be 8 words, and he told me that it is only 4 words.. and then I remembered that it was a 12 word split up instead of a 24 word split.. and so when he read me the 4 words, he mentioned that one of the words was "xxcxxxxx", and I said that does not even sound like a real word, and he read it several times and told me that is what it says. I said o.k... so I wrote down the 4 words, and I told him that I would let him know if I had any problems in terms of getting access to the wallet that I was wanting to get, but I would have to do it in a few hours.
So when I put together all 12 words, and I typed in the "xxcxxxx" by the time I got to the second letter, there was already a suggestion that had the word to be "xxrxxxx".. so my friend could have had sworn that the word the one with the "c" and neither of us even thought about the word with the "r".. so sometimes simple mistakes can be figured out, but some kinds of more complicated mistakes might be a lot more difficult to resolve.
...
You should not split up a seed. someone finding one piece compromises the whole encryption.
Also you often have to get your seed words through communication channels (in your case phone) which has the risk of a middleman attack.
If you want to produce shares to give to friends I highly recommend using Shamir (Model T) where every share in itself is totally worthless and doesn't compromise the security when found. It's a kind of prestage to multisig which requires several wallets but can be manufacturer independent. (so for me Shamir is the second best when it comes to security)
It's very easy to use and might be perfect for what you want to do.
BTW afaik:
the reason for 24 words instead of 12 is actually that even if someone knows all words (out of order), your coins are still secure.
If someone knows all words of a 12 word seed out of order, he can brute force the sequence and get your coins.
If I remember it right, back in the days there was no option to put your seed directly into the Trezor so you had to use the keyboard on your computer. The computer didn't know the sequence though, as you were asked to put in the words out of order (for example word 7, 2, 11, etc). But with a 12 word seed someone could know the out of order words via a key logger and steal your coins by brute forcing the order.
That means you could send your 24 words through any compromised communication channel (even post it here). And as long as no one knows the word sequence, your coins will be fine.
