To be clear, we recommend that you connect to Wi-Fi. If you are on a Wi-Fi connection, the amount of data that the app is using is probably irrelevant, as it is free and unlimited. The amount of data used is really only relevant when you are using your device's data plan.
To know exactly how much data a voice conversation consumes, you need to know which codec the call is using to communicate. UniTel Voice's system negotiates calls across different codecs, depending on the underlying networks involved. (A codec is a compression engine that transforms your analog voice into digital data.)
Below are some approximate values for data consumption of the most common codecs used for VoIP:
G.711 - 87Kbps
G.729 - 32 Kbps
Based on these numbers, we estimate that a typical phone call can expect to use about 0.75 MB per minute. So, if you plan to talk for an hour, you would use roughly 45 MB.
To put that into perspective, most cellular customers have plans that cover 2 GB (gigabytes) of data per month. For every HOUR (60 minutes) you use the app, you would be using 2.25% of your data plan.