What does the AT&T data plan include?

I'm going to get the 15 dollar data plan for AT&T with my iPhone. I know what it kinda includes but can you give me recap? THE MOST IMPORTANT QUESTION I HAVE: How much minutes and text messages can I send!
Is internet free when I use it at home? Like would my data go away for using Wi-Fi i have connection to?

First of all the plan you are talking about is the 300mb for $20. This includes 300mb of data. You can use it however you like. Just be aware that if you go over this plan they will charge you another $20 for 300 more mbs. As for minutes this is only a data plan so it will only provide you with data. You can choose your plan of minutes and messaging by going on www.att.com. Or by dialing 611 from your handset. You also can go into your local at&t store and they can explain all the plans for you. If you tell them how much you talk and text they should be able to provide you with a plan that suits your needs. As your your home internet it is free for you to use it on your handset. The great thing about this is its unlimited. When your phone is connected to your home internet any data that your phone uses will be done over your unlimited internet in your house.At&t data will only be used when no Wi-Fi is available but trust me you can pretty much find Wi-Fi anywhere these days.At&t has nothing to do with your Wi-Fi. The only time your data plan will be used is when your arent connected to Wi-Fi. One more thing depending on what phone you have, you can shut off the cellular data and this will restrict all data usage to Wi-Fi. Thats what I do. I have the lowest plan on my iphone and i only use my cellular data in emergencies. Just a note that multimedia messages like pictures and stuff will not come through if your cellular data is off. Hope I helped.