Seems to me it might be cheaper if your speakers are in good shape to change the head to a new one which accepts a jack. That's what i'm doing because between Pandora and all my CD's on the Iphone I don't need no stinkin radio or CD player. They are pretty cheap right now.
Usually they don't, you will have to do a bit of googling. The amp also needs the signal lead to be hooked into a 12v power source (make sure you add a fuse to this lead, and a switch so you can turn the amp on and off). It's not that difficult to do, just takes a bit of brain power and some research first.
All it has is male micro-jack for input. It's kind of cheap and generic but it does a pretty good job. It ain't exactly high sound quality but volume is good. I remember being ticked off when I first bought it because the sound volume was barely audible. I cursed and stomped thinking I got ripped off and then realized the volume on my iphone had to be turned up. Been happy with it since then.
1994 YJ Wrangler, 4.0, AX15, NP231, 35x12.50x15 BFG KM2s, 4" RC lift, 1" lift Boom Shackles, 1" BL, 4.10 gears, 8.8 LSD in rear and D30 Aussie Locker in front, on-board air conversion, Ramsey RE8000 winch.
A really good place to look is towards marine amps. They also have a lot of radios with either non-standard sized head units, or surface mount remote controls. A hidden mount control box and a small remote volume and mini controller is a great way to go. Even if you want a standard dash radio, Crutchfield has a few great marine units that can even stream via Bluetooth!