The REOL: Realtime Estuary and Ocean Logger is a water quality sonde that measures water properties and sends them in realtime over the mobile phone network using a cellular modem. The result is a live display of measurements from any region where cell phone towers can be found. The project is entirely Open Source and the goal is to produce each instrument for less than $1000. This makes the REOL accessible to a much broader user community than most oceanographic instruments. The current version measures water temperature, water depth and specific conductivity. However, the platform can easily be adapted to measure dissolved oxygen, pH and other water properties. In June 2014, we successfully used the REOL to measure salinity in a hypersaline estuary in West Africa using the Orange™ mobile phone network.