Still, I'm signing up with T-Mobile soon and I'm likely to try this myself. :)
Apparently the text that it violates is: "Your five numbers must be US domestic numbers and must not include ... customers' own numbers; and single numbers allowing access to 500 or more persons."
I think you can easily get away with having your own Google Voice number as a MyFave. That number is unique to you and shouldn't set off red flags. What I think may be a bit more sticky is the 347-234-5001 number, which, if GV continues to take off, might get noticed because a lot of people will be "fave-ing" that specific number.
Just something to think about. I'm not sure yet if that thought is going to deter me or not from doing it myself. I'm leaning towards "no". :)