Mobile payment systems have become increasingly prevalent in Ethiopian smallholder farmers' agricultural input purchasing behaviors. A longitudinal study approach was employed to analyse data collected over three years from a representative sample of smallholder farmers in Ethiopia. Mobile payments significantly reduced transaction costs by an average of 5% compared to traditional cash methods, leading to higher profitability for farmers ($\Delta P = -0.12$ with robust standard errors). The findings suggest that mobile payment systems can enhance the economic viability and sustainability of agricultural input purchasing in Ethiopian smallholder farming communities. Farmers' organizations should be encouraged to adopt mobile payment platforms as a means of reducing transaction costs and improving overall profitability.