In mobile telephony, one of the first things new hires are told is “don’t even try to work out what all the acronyms stand for; it won’t help”. You just have eat all the alphabet soup. Worse is that they nest themselves. You can have acronyms where every letter stands for another acronym. Writing a thousand words without using a single noun is easy. And of course all the short ones are overloaded. Is an AP an Application Processor or an Access Point? Depends on which subfield the person you’re talking to is from.

But they’re a necessary evil, since MSISDN is still less cumbersome than Mobile Station International Subscriber Directory Number.