Unless you use aftermarket software to scramble the data, someone could theoretically get user data after a wipe. The easiest way I have found to hide my data permanently is to- 1. wipe data 2. load useless data until storage device is full 3. wipe data -repeat until you are less paranoid. I have found usually 3 cycles of this is 100% overlap of all existing data;
the theory is that anyone can retrieve wiped data which has been recently "wiped" because it is essentially just placed into the "to-be-overwritten" partition, which will remain in tact and retrievable until it has been overwritten by something, something big usually is most effective.
e.g.
When I broke up with my X I asked for my pc back and my x-girlfriend wiped/formatted my pc's hard drive after we broke up- because it was a recent format, I was able to retrieve EVERYTHING that had been formatted. Everything. (except the files which were overwritten due to reinstalling a fresh windows os- which was only about 1GB).
Oh yes and I forgot to ADD that Cell Phone Carriers are supposed to "factory reset"/"wipe" all returned phones upon receiving from users- that's policy. So in reality, unless you are a criminal or a secret agent hiding your data from cell phone carrier is ridiculous, they aren't going to investigate your phone data, now, if you are a criminal or secret agent and the FBI gets your phone, then you might be in trouble- but I believe even my method can thwart the FBI.