Facetime? IPhone 4s? Data Plan?

Okay, so i moved a few weeks ago and we don't have internet yet. So i use my data plan wisely when on instagram or anything. So when i'm connected to Wi-Fi when i go somewhere, does facetime use up my data plan? Or not? Same with oovoo. If i'm connected to Wi-Fi how much or fast will it use on my data plan?

Streaming any kind of video uses a lot of data so it will consume your data plan really quick. When you're on Wi-Fi turn off your cellular data just to make sure your network doesn't use any on the side but while on Wi-Fi you don't use cellular data.