Texting with an iphone through Wi-Fi?

I have an iphone 4, but with no data or credit. I can text other iphones through the Wi-Fi with imessage, but now some won't send. Do they have to be on Wi-Fi to receive the text? Or if they're on 3G will i still be able to text through Wi-Fi?

They will receive it whether they are on Wi-Fi or on a Wireless Data Network.

"Do they have to be on Wi-Fi to receive the text?"

If you're sending through Wi-Fi, they should be able to get it through the internet no matter how their phones are connected.

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