This paper deals with optimization techniques that can make very large vocabulary voice dictation applications deployable on recent mobile devices. We focus namely on optimization of signal parameterization (frame rate, FFT calculation, fixed-point representation) and on efficient pruning techniques employed on the state and Gaussian mixture level. We demonstrate the applicability of the proposed techniques on the practical design of an embedded 255K-word discrete dictation program developed for Czech. Its real performance is comparable to a client-server version of the fluent dictation program implemented on the same mobile device.