SuperNanny has suggested that the parent help the child give the bottles away to a baby. Talk about how babies need bottles and now that he's a big boy perhaps he'd like to give his away. You can have a ritual around it.
My daughter switched her kids to water in the bottle. When they were ready they switched themselves to a sippy cup. She provided both. Every once in awhile she'd suggest taking the sippy cup and eventually they did. They did drink from it at times during the night. I think it's a good way to get water into them and makes for better sleep because they aren't thirsty.
When the oldest was around 3 I found travel cups in cheerful colors. They were leak proof but easy to use. The kids used those for another year or so. They stopped when they forgot to get them and Mom enforced the rule that once you're in bed you stay in bed. For awhile getting them was part of the bed time routine.
I prefer a gradual change. He is most likely using the bottle as a source of comfort. Cold turkey feels just a bit cruel unless you give him something else to use for comfort.