Upvote:3
I see two relevant possibilities for a Brazilian citizen to bring goods bought outside the country in this specific case:
About your second question, how can your friend prove (s)he had something before leaving Brazil, the offically suggested way is to have a reputable document (such as a Brazilian invoice) of the product which is given when the product is bought. Showing history of calls (or something like that) is not guaranteed to be accepted (even though authorities have some discretion when deciding what will be considered a personal good). Anecdotally, people where buying stuff like laptops and loading the hard drive with an image of an operational system with lots of (old) files, as a way to "prove" it was previously owned.
There was a time when you could show up in the Receita Federal (the government service that is responsible for taxes, sort of like IRS in the USA) and present your goods before departing. They would give you a document stating that you had such items before departing, but this is not happening anymore.
Just for the sake of completeness, here is a link for the official "traveler guide" for Brazilian citizens. It states all the currently valid rules and exemptions one might use. You friend better read it carefully so he knows all the details.