There are two lags to take into account. Lags at connection, and lags during the call. Connection is what is very complicated to do safely, but once its setup,

There are two lags to take into account. Lags at connection, and lags during the call. Connection is what is very complicated to do safely, but once its setup, except for some signaling, it is much simpler [1]. The architecture used by some people (I wouldn't know exactly who does what, it's all muddy) is that the connection/signaling is done in application processor, but the Encoding/Decoding + RTP is done in baseband processor. You do get a bit of additional of lag at connection (but anyway you have an UI to show), but you can keep your real time audio guarantees. [1] That's for volte. For vowifi, that's more complicated, but anyway talking about lags over wifi...