Explanation: The two most-used Personal Communications Systems (PCS) coding techniques for separating different calls are CDMA (Code Division Multiple Access) and GSM (Global System for Mobile Communications). **CDMA** allows multiple users to share the same frequency band simultaneously. Each call is assigned a unique digital code, which is used to spread the signal across a wide bandwidth. Receivers then use the specific code to extract their intended signal from the composite noise-like signal, effectively separating calls without requiring different frequencies or time slots. **GSM** primarily uses TDMA (Time Division Multiple Access) and FDMA (Frequency Division Multiple Access) for call separation. FDMA allocates different frequency channels to different users or cells. Within each frequency channel, TDMA further divides the channel into distinct time slots, allowing multiple users to share the same frequency by transmitting during their assigned time slot. Options A (QPSK and QAM) are digital modulation techniques, which define how data is encoded onto a radio wave, not how multiple users' calls are separated. Option C (ABCD and SYZ) are not standard telecommunication terms. Option D (AM and Frequency Hopping): AM is an analog modulation technique. While Frequency Hopping Spread Spectrum is a multiple access technique, CDMA and the TDMA/FDMA methods employed by GSM are the predominant "coding techniques" for call separation in modern PCS.