I still need help, if somebody knows the answer to my question, please post it here!!
The question is 'What does 'fat middle' mean?', and the short answer is 'I don't know'. This is a blog about mobile telecoms, and those guys speak a language of their own. (I used to teach a Vodafone employee, and helped her with her presentations. I found the jargon of that business quite opaque.)
It may mean that if a certain distribution - say, of customers for mobile telephones - forms a 'bell curve', most of the business relates to the middle of the curve. But I really don't know.