Text messages use your data connection, however, the amount of data usage is significantly less than that of a voice call.
The voice calls are made over your data connection and consume 6 kilobytes per second. Another way to look at it is 1MB for a 3-minute call. Therefore, if you are using your device on a cellular network, the call will consume some of the data allowance from your cellular data plan.
We strongly recommend that you are connected to wi-fi if using Sudo for frequent calling and messaging so that you do not incur excess charges on your cellular data plan.