My 454SS has had a PreAmp setup with an audio input jack for roughly 20 years. The input jack was only connected when I got my first ipod (about 2007), but it is just thru a pair of RCAs. It has a radio/cd changer control/etc, but the radio poortion has never really been used (I only used the CD changer back in the day, but it isn't even in the truck anymore). The unit is a Pioneer DEX-M400. They haven't made it for many years, but I ended up with 2 of them. I have one in my SS and one in my '66GTO. I really only use the ipod or my iphone for all source input, and the preamp for equalization. Can listen to many audio sources via the iPhone apps.
I currently use a device called a Tunelink (New Potato Technologies) to get the data via Bluetooth to my Stereo input jack. It works great and does not require the use of an app. I use it in my company vehicle that only has a stereo input jack. My iPhone's audio plays wirelessly to the stereo, as well as navigation commands, etc. It does not do the audio for a phone call, but when the phone rings, it mutes the music and then continues where left off when the call is ended. I am not a fan of bluetooth phone calls due to poor quality sound on the other end, so this works great for me. I have used this in my truck as well, but plan to add the following unit as a more permanent solution.
A fairly new device that can convert audio via bluetooth, but has volume & track forward controls and mounts in a 3/4" hole (cig lighter plug comes to mind). I am in the process of getting setup to be a dealer on this product mainly for all the classic car audio work I do as well as boats. I can see this device working very well and will be getting my hands on one soon. I will install it on my GTO where the cig lighter is and supposedly the knob can be removed, so I will put the OEM style 1966 GTO knob so it looks factory.
http://www.wetsounds.com/pages/products/WW-VC-BT.html
I like OEM appearance, but aftermarket quality. This gives the ability to leave the phone in my pocket and just use the knob to change tracks or turn up/down the volume.