I don't claim to an expert in telephony, and there well be some holes in my description, let me provide at least one take on the issues, problems, and possible solutions. The different possible character sets are not really an issue for us here in the simple format and information being exchanged. Along came the first computer nerds, they decided to replicate that action in their electronic coding. AS IS, i.e., you must use bin or binary mode.
Some people say when in doubt , use bin mode.