It's an interesting problem, let me throw my two sats here for some practical addressing to these problems (that means no IPoAC or Skylink, sorry guys

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In the case of radio, you could just convert the transaction bytes to morse and broadcast an (english or other languge) START TRANSACTION and END TRANSACTION codes, but its possible for some of the waves to get lost or distorted - it is basically an old-fasioned form of UDP.
So there would have to be checksums around the morse code to prevvent any of the bytes from being lost or corrupted. Not like a few bytes at the end, but redundant data carried around other packets, probably XOR'd together. Or like how QR codes do it.
SMS doesn't have this problem obviously, but it would have to be sent from a specific sender for it to be trusted.
Otherwise, any random bloke can submit a garbled or fake transaction.
Being a structure of bytes also, blocks can be transmitted in much the same way as transactions, only much larger.
why would the sender have to be trusted? it's only a transaction. you could send the signed transaction data via text to anyone in the world who has an internet connection, all they would then have to do is broadcast from a node. there would be an incentive for people to set up anonymous nodes specifically for this purpose. you would just have to set up a node and provide a few mobile phone numbers for receiving transactions. you could also set up a virtual office to receive transaction data physically but that would be insane.