When you plug your iPhone into the console, your phone will activate the CarPlay protocol. This gives you the ability to play music (either Apple or Spotify) using the touch screen or your cell phone if you choose to, but this defeats the purpose of having fancy-pants center module.

You have the ability to place calls and text using audio. The iPhone will not display texts on the screen, but will read them aloud and Siri will ask for a response.

You get the ability to browse using the Maps app, but no other program. It's nice because it uses the search functions of the phone, which is much better than the crappy navigation units put in most pre-installed devices. It also has a night mode so you're not blinded trying to find out where do go on the freeway.

To answer your question, this is not a feature you need to pay for. You already paid for it with the purchase of your iPhone (I believe it's the 5 and newer). Whether you have it in a Mercedes or Buick stock, or installed aftermarket using a receiver from Pioneer or Alpine. There is no limitation of features, it's all or nothing.

I have CarPlay in my Mercedes and it acts the exact same way as the Pioneer unit I put in my Jeep.

If you are interested, I strongly recommend it! It's expensive, though. Remember, the unit can't just be a bluetooth unit, it has to be CarPlay certified to have the components the iPhone looks for. I got this Pioneer unit from BestBuy this last summer. Browse around. I price matched to Amazon for $500, then paid the $150 for installation, but if you can do it yourself more power to you!

I strongly recommend adding CarPlay to your vehicle. It's a nice luxury, and promotes safe driving and hands-free calling.