Hi Jennifer!
Our pediatrican encouraged us to use the cold turkey route. Just take away the bottles and eventually the kids will drink out of the sippy. Our daughter had a tough time and cried a lot, but by the next day she was thirsty and drank from the sippy - and never looked back. With our second child, we started him on a sippy cup around 9 months with water to teach him how to use it so the transition was easy when he turned 1.
But, it's like letting kids cry it out at night - some people are comfortable with it and some people aren't. It's definitely a personal choice. I wish your friends the best of luck!!!!
Michelle
Michelle Sussman
www.michellesussman.com