A universal technique for transmitting data over voice (DoV) links that can be applied to various cellular networks is proposed. In the scheme, a generic modulation model is established based on waveform symbol mapping, where the data to be transmitted are mapped into finite waveform symbols of a codebook generated offline and demodulated with soft decision results at the receiving end. To make the proposed scheme applicable to various kinds of cellular networks, first sinusoidal signals are selected to synthesise waveform symbols due to their stable transmission characteristics over various voice channels. Then, an analytical method based on Surface Packing is proposed to optimise modulation codebooks. Finally, the target demodulation codebook is obtained through learning from the modulation codebook online. Simulation results show that the proposed scheme performs well over voice channels with different vocoders and has low symbol error rate on various vocoders. Compared with previous schemes designed for some specific vocoders in global system for mobile communication (GSM), the proposed scheme can extend the application scope of DoV to cross‐network scenarios consisting of GSM, universal mobile telecommunications system (UMTS) and long‐term evolution (LTE).