Does messaging to/from iPhone to/from iPhone/iPad/iPod Touch count as a text charge for Verizon?

Question

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!

Answer 1

I then turned Wi-Fi off on the iPhone 4S but had "Send as SMS" turned on, tried sending another message to the Touch (Wi-Fi activated), and it did not send at all (because the Touch is SMS-incapable).
That sort of makes sense, but even with wi-fi off the 4S should have been able to send the iMessage over 3G to the Touch, which was on wi-fi.  Your results would only make sense if the 4S didn't have 3G service, or if the iMessage servers were down, or if you've turned iMessage off completely on the 4S.  That would force the message to go out as SMS but the Touch can't receive SMS.
Sorry, I was a bit unclear there.
I had both Wi-Fi and Cellular Data (3G) turned off to see if "Send as SMS" alone would work if I was sending a message to an SMS-incapable device (to see if the iPhone would try anyway and to see if I would get charged for that).
I'll type out some scenarios, and tell me if I'm wrong on these. They might seem redundant since you have pretty much answered all my questions, but I want to make absolutely sure that I understand. These could also clear things up for others who will/have read this discussion.
Scenarios involving iPhone 4S to iPod Touch (both running iOS 5):
4S has Wi-Fi, 3G, and "Send as SMS" turned on. Touch has Wi-Fi turned on.
4S can iMessage to Touch via Wi-Fi (as long as there is a Wi-Fi signal) free of charge and will remain free of charge and with no accrued data usage because 4S prioritizes Wi-Fi before 3G before SMS.
Once out of range of the Wi-Fi signal, 3G kicks in and any iMessages sent from 4S to Touch will count towards data plan usage (in my dad's case, 300MB/$20 per month - the minimum plan). However, data size will be insignificantly small if it's a simple words-only message and will only be a fraction of a percentage of the 300 MB.
My dad turns off Cellular Data (3G), Wi-Fi is still out of range, and he sends a message (keep in mind that "Send as SMS" is still turned on). Because the Touch is not capable of sending/receiving SMS messages, the message will just fail to send.
These scenarios would also have the same outcome if the Touch had been a Wi-Fi-only iPad. If the iPad had 3G capability, the message received from the 4S would have added towards the data plan usage of the iPad.
Scenarios involving iPhone 4S to another iPhone (both running iOS 5):
Both phones have Wi-Fi, 3G, and "Send as SMS" turned on. Messaging plan for each phone is "Pay as You Go" - $0.20/text and $0.25/picture or video.
iMessages are free and do not count towards data plan usage if both currently have strong Wi-Fi signals.
4S still has strong Wi-Fi signal, other iPhone gets out of Wi-Fi range and switches to 3G. Any messages received by the other iPhone from the 4S will count towards data plan usage of the other iPhone. However, the outgoing message from the 4S will still be free and will not count towards data plan usage.
Other iPhone turns off 3G and is still out of Wi-Fi range but still has "Send as SMS" turned on. 4S (with strong Wi-Fi signal) sends message, "I love you." to other iPhone. The message will still be free and will not count towards data plan usage for 4S but will charge $0.20 to other iPhone.
Scenario involving iPhone 4S to Samsung Galaxy 2 (running Android OS):
4S has Wi-Fi, 3G, and "Send as SMS" turned on.
Any message sent from 4S to Galaxy will count as SMS because Galaxy is incapable of iMessage. Therefore, Wi-Fi and 3G are insignificant, and 4S is charged $0.20.
4S has Wi-Fi, 3G, and "Send as SMS" turned off.
4S will not be capable of sending anything.
4S has Wi-Fi and 3G turned on, but "Send as SMS" is turned off.
4S has strong Wi-Fi signal, but message will not be sent to Galaxy.
4S gets out of Wi-Fi range and 3G kicks in, but message will not be sent to Galaxy and no data usage will have occurred.
That should be everything...at least everything I've considered.
Again, thank you.