I've also started testing this phone hack, and so far-so good....except, like Pearl said, setting the ringer does not work. (I'm playing in Uni right now) I tried deleting all the phones in the dorm, and re-buying them, and then setting the ringer, and that still did not work.
At one point, when my Sim went to sleep, the phone rang constantly for like 7 hours straight on high speed!
She was able to call the Taxi and invite friends over just fine. She talks to others on the phone until she's ready to hang up, meaning that she spoke past the time the Daily hit 100.