Speech encryption is becoming increasingly important as the increasing relevance of multimedia applications such as video conference and news broadcasting. However, multimedia encryption and decryption are often computationally demanding and unpractical for power-constrained devices and narrow bandwidth environments. It is a challenge to obtain a good tradeoff between high security and low computational cost. To tackle this situation, a group of hierarchical selective encryption schemes are presented based on the computational complexity analysis of G.729 standard speech in this paper. In the proposed schemes, speech bit streams are partitioned into two parts according to the bit sensitivity, i.e., one is encrypted by a strong cipher and the other by a lightweight cipher. The contrast experiments are addressed in signal inspection and objective distortion measure. Additionally, we discuss the schemes' cryptanalysis is investigated. The results demonstrate the effectiveness of the hierarchical selective encryption schemes for power-constrained devices and narrow bandwidth environments.