If you plan to use an ATM integrated access device to carry voice calls as well as data, you need to consider the compression used on your voice calls.
Several standards exist, offering varying levels of quality and bandwidth usage.
At this rate, a full ATM DS-1 can be filled up after only about 20 calls, with no room left for data traffic. By sampling less often, an analog signal can be reduced to between 16 Kbps and 40 Kbps, depending on the quality you desire. Voice quality can seriously degrade as the sample rate gets lower. Because the IAD is sampling the analog waveform less often, sounds can be completely left out if they occur between any two samples, giving signals a muddied quality. While G.729 sounds great, offering good quality at low bandwidth usage, there are trade-offs.