The SmolPhone project explores the design space of modern smartphones with energy limits, increasing the battery lifetime possibly at the price of a reduced feature set. The energy consumption of classical smartphones can roughly be divided in three main parts: the processing units, the screen, and the network connectivity. This paper evaluates the practical feasibility of the SmolPhone vision, which involves heterogeneous multiprocessors and low-power technologies for the screen and network. We identify several usage modes according to the provided features, and quantify the energy consumption of the processing units in each mode, as well as the time required to switch between modes.