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

a blue message is a non-SMS message, it is an imessage and counts toward data only (i.e. essentially free)

imessages do use data when connected to the cell network, but the data usage is so small that you will never be able to text your limit

When are messages free, and when are they not free?

They are free if iMessage, not free otherwise.

Are they free as long as there is a Wi-Fi signal?

iMessage over wi-fi is free (assuming you have access to free wi-fi). iMessage can also go over 3G if wi-fi is not available, as long as 3G is available and as long as the recipient has iMessage. As noted above, the data used is tiny so essentially no-cost over 3G, unless pictures are attached to the iMessage and they're sent over 3G. But if wi-fi is available, iMessage will use it.

Are they free as long as it is from the iPhone to another iPhone/iPad/iPod Touch?

Yes, only these devices support iMessage. A text sent to a different device will go out as a regular SMS text. Note that iMessage will go out as SMS if the iPhone/iPad/Touch don't have iMessage turned on, or if the iMessage servers are down (probably rare). In that case you can set the iPhone to NOT send messages as SMS if iMessage is not available -- I suppose they'd just sit in limbo until the servers come online. Not sure what'd happen if the recipient had an iPhone on iOS 4 which doesn't support iMessage, would probably go out as SMS.

Do I get charged for data only when I see the "3G" symbol displayed in the upper left corner of the iPhone?

Yes, but the data over 3G is small unless pictures are embedded into iMessage.

I tried sending a message to the iPod Touch (while having the Touch disconnected from any Wi-Fi signal) from the iPhone 4S (using Wi-Fi) with "Send as SMS" turned off, and the messages were in limbo until I reactivated the Wi-Fi signal on the Touch.

Yes, that would make sense -- since the Touch can't do SMS, the message will sit in limbo until the Touch gets back onto wi-fi.

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.

So, what you said here - "Note that iMessage will go out as SMS if the iPhone/iPad/Touch don't have iMessage turned on, or if the iMessage servers are down (probably rare)." - is partially incorrect (no offense). You've been really helpful.

None taken, and you're quite right and I wasn't paying attention to all the details.

One more question (if you don't mind): Under "Send as SMS," it says "Send as SMS when iMessage is unavailable. Carrier messaging rates may apply."

Does this "Send as SMS" option also imply "Receive as SMS." That might be a dumb question, but oh well.

Receiving an SMS message will always cost you (unless you're on an unlimited plan) but I think what you're getting at is if you have two iPhones both set to use iMessage, but if iMessage is unavailable then what happens? In that case the message will go through as SMS.

In your dad's case, if he sets his iPhone up to not use SMS if iMessage is unavailable, he'll still receive SMS messages from non-iPhones, and SMS messages from iPhones when iMessage is unavailable, but obviously he'll never receive an SMS message from a Touch or wi-fi only iPad.

Hopefully that helps (and hopefully I didn't screw anything up!)

Your scenarios look correct, except:

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.

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.

In this case I don't think the message from the 4S will go out as iMessage since the recipient has no 3G or wi-fi. If I'm not mistaken, the iMessage servers will respond that the recipient is not available, so the message from the 4S will go out as SMS.

Scenario involving iPhone 4S to Samsung Galaxy 2 (running Android OS):

4S has Wi-Fi, 3G, and "Send as SMS" turned off.

4S will not be capable of sending anything.

Actually, I think the 4S will always send SMS to a non-iPhone, regardless of the "Send as SMS" (when iMessage is unavailable) setting. Again, somehow the iMessage servers know that the recipient is unavailable (or in this case, never available) so the message will always go out as SMS.

Scenario involving iPhone 4S to Samsung Galaxy 2 (running Android OS):

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.

Again, because iMessage servers know that the recipient cannot receive iMessage, all messages from the 4S to the Galaxy will always go out, and will go out as SMS. The "Send as SMS" setting is only in context for iMessage, so all messaging will always be SMS to devices that can't participate in iMessage.