Human ear cannot generally perceive mouth-to-ear delay under 200 milliseconds.
If you perceive a delay during call, chances are that is between 300 and 500 milliseconds, which is perfectly acceptable to have a conversation on phone.
Higher delay in the order of 1-2 seconds (such as satellite communications) makes phone call more difficult, but still doable with some practice.
There are two main causes for perceivable delay using EVSS:
|2G||500 - 2000 ms|
|EDGE||2.5G||200 - 500 ms|
|3G||3G||100 - 300 ms|
|HSDPA||3.5G||100 - 300 ms|
|LTE||4.G||100 - 200 ms|
While GPRS provides enough bandwidth for PrivateWave to play crystal-clear audio, it exhibits a high jitter, which introduces a perceivable delay.