My dad has an iPad 2 and my little brother has an iPod Touch (4th generation). As long as there is a Wi-Fi signal, they are able to message, Facetime, and use the internet all for "free" (no extra charges from our internet service provider, which is obvious).
My dad recently purchased an iPhone 4S from Verizon.
He is currently on the "Pay As You Go" plan for messages ($0.20/text and $0.25/picture and video).
When are messages free, and when are they not free? Are they free as long as there is a Wi-Fi signal? Are they free as long as it is from the iPhone to another iPhone/iPad/iPod Touch? Do I get charged for data only when I see the "3G" symbol displayed in the upper left corner of the iPhone?
Thanks in advance!