Perhaps you can go to the Telmex site and see if they have a terms of agreement for internet use. Most likely the answer your friend got was made up on the fly, though it could be true.
Living in Mexico, I can comment that the law is very different here than the US. There are laws on the books, but the actual system in use has little to do with the laws and much more to do with interpersonal politics and how much money any given law enforcement agent feels that he needs at the moment. It is always and constantly negotiated on the fly. You can obey all possible known laws and be attacked by the law for invented or imagined infractions in any case.
You also can break almost every law in the book and be totally ignored if nobody sees you as a target for income. They just don't work the way we do.
One example would be driver's licenses and license plates. The law,just like in the US requires these. In my area, almost none of the local drivers has a license and the police don't enforce it. One is simply foolish to bother. There are no tests and if you want a license, you buy it. Plates are typically used, but it's up to the officer and none of the motorcycles use them here - the motorcycle drivers are mostly kids under 16 years old. I've seen 14 year olds driving big trucks.
The only time I was fined here was for doing a right on red. I told the officer I thought it was legal in Mexico like the US, he said it was not and fined me. I looked it up later, and it IS legal. On the other hand, all the taxi drivers run the red lights, and the police don't care. Extremely dangerous.
So, good luck sorting out what written law is and remember that it does not apply.
Personally, I'd just do it and be discreet. I know that goes against many folks here who feel more certain about what's right and wrong, but I doubt they live in Mexico.