Ok, this may be kind of embarrassing because I don't know how many 4 year olds still use a sippy cup... but mine do.... well, until recently.
Our routine is I make 4 sippy cups of Carnation Instant Breakfast every morning with the kids oatmeal. The kids need calories! Jadon and Kaylee get whole milk (they need more calories) and Addison and Cody get skim milk.
Once the milk is gone, I clean one cup and fill it with ice water which they share all day. Drinks are not allowed upstairs, but you will find them in any number of places downstairs. So, we like lids and spill proof.
Well, recently we started introducing cups at lunch and dinner. At lunch I let them drink a fruit/veggie blended juice and at dinner they get a cup of milk. The rest of the time it's water from a sippy cup... but we have actually graduated to cups in our home. Even Cody who is almost 3 is using a cup. The change hasn't been implemented without spills and messes, but they have been minimal and they all seem to be doing well.
If it were up to me, I think I'd send them off to College with sippy cups... Hey, I'd make sure it had their college emblem on it....