Digital technologies such as Time Division Multiple Access ( TDMA ) systems build upon the AMPS framework, using the subscriber unit, base stations, and MTSO in a similar way. However, TDMA adds capacity to the system by letting multiple users share a radio channel without interference or sacrifice of voice quality. TDMA technology makes it possible to serve subscribers on each radio channel by converting speech sounds to a stream of digital information. The voice is sampled and compressed by a vocoder. The resulting 8,000 bits per second represent the voice. The speech data is compressed into bursts only a third as long as the original audio signal. The encoding, transmission, and decoding are nearly instantaneous, so the remaining time is left for other subscribers. To share the airtime on a radio channel among multiple subscribers, each subscriber sends and receives bursts at separate times. The times are allocated as slots of one 150th second, and assigned among three subscriber's. Subscriber's communications are timed precisely to assigned slots. A digital phone receives the digital information and expands it to a full stream. The expanded data is decoded to reproduce the original voice signal. Digital transmissions are inherently private because scanners are not equipped to decode or time-align with the digital bursts. Digital transmission are easily encrypted to make eavesdropping nearly impossible. TDMA is also the technology base for ( NADC ) North American Digital Cellular and JDC ( Japan Digital Cellular ).

GSM is a TDMA digital system that converts voice and access information to digital data, and communicates those data in bursts during brief time slots allocated to multiple subscribers sharing a radio channel. Like other digital technologies, GSM encodes, transmits, and decodes bursts in a fraction of the time required to produce the sound, using only a fraction of the air time on a radio channel. GSM uses radio frequencies about three times as efficiently as TDMA. GSM voice compression differs slightly in using more bits to represent a voice signal, and compressing voice information fivefold. GSM has no control channel, using only one type of 200 kHz traffic channel for voice and access. GSM phones can select cell sites and channels when initiating a call or during a call, and they assist hand-off by measuring channel quality of nearby cell sites. GSM's digital format allows advanced encryption techniques, strongly securing calls against eavesdropping.

GSM phones use a removable Subscriber Identity Module ( SIM ) card containing the phone number, secret key, user's personal portfolio of services, and authentication algorithm for validation.

Code Division Multiple Access ( CDMA ) serves multiple users on a single radio channel. Technically, CDMA differs from TDMA in three important ways, CDMA radio channels are about 6 times wider, the system assigns each subscriber a unique pseudo-random noise ( PN ) code. The subscriber unit then enhance signals carrying the assigned code, leaving the other signals inaudible. CDMA has the potential to serve more users per channel than TDMA or AMPS. The 20 -fold increase in system capacity is approximate. No fixed subscriber capacity can be assigned to CDMA systems, because their capacity depends upon the ability to control the power levels of the phone. Because of the power levels, fewer subscribers can be served. The bits sent along each communications path are assigned a unique code, to be sure that enough information gets through to accurately describe the voice, each coded bit is repeated many times and are mixed into a radio channel with bits from other communications paths. To accommodate heavy traffic, CDMA systems can vary the speech coding rate and accept higher bit error rates, but eventually, if to much data crowds the channel, the signal quality deteriorates. CDMA hand-offs also differs slightly from other systems because it allows the subscriber unit to simultaneously monitor and communicate with multiple cells, making hand-off less noticeable.