The proliferation of mobile applications (apps) has made it crucial to ensure their accessibility for users with disabilities. However, there is a lack of research on the real-world challenges developers face in implementing mobile accessibility features. This study presents a large-scale empirical analysis of accessibility discussions on Stack Overflow to identify the trends and challenges Android and iOS developers face. We examine the growth patterns, characteristics, and common topics mobile developers discuss. Our results show several challenges, including integrating assistive technologies like screen readers, ensuring accessible UI design, supporting text-to-speech across languages, handling complex gestures, and conducting accessibility testing. We envision our findings driving improvements in developer practices, research directions, tool support, and educational resources.