It does both.
The change from liquid to solid is exothermic, and the change from solid to liquid is endothermic.
If you melt ice and measure the temperature you will notice that it flattens out at 0°C as the heat energy is being given to the molecules that are liquid. Ie at 0°C you can have 100% ice, 100% liquid water, 25.467% ice 74.533% water etc.
In the above two examples they will stay as they were, if the whole lot of water was 0°C then it would stay the same but due to variances that wont occur and you will have an equilibrium H<sub>2</sub>O<sub>(s)</sub> <----> H<sub>2</sub>O<sub>(l)</sub> ΔH= -ve
