If I have Wi-Fi on my iphone and I have cellular data on do I get charges for data?

For whatever crazy reason my iphone 4 won't send pics unless its over Wi-Fi through an iMessage to another iPhone or I have cellular data on to send it to a not iPhone phone. I just turned the cellular data even though I had Wi-Fi so I could send a pic. Did this cost me data?

No, it does not. If you are hooked up to Wi-Fi you don't use any data.

Sending pictures over cellular uses a lot of data, if you want to send pictures to other phones try changed your plan so that is included.

No. That is why people use Wi-Fi.