This dock isn't perfect- the remote will control volume, but nothing more. (I'm using an iPhone 3GS - YMMV.) Also, the infamous "not designed for iPhone" message comes up when you cradle a 3GS, but you can click "No" (so you don't go into flight mode) and it still works. The audio DOES work, and, with this easy little mod, the cradle will charge your iPhone while its docked. All for less than $15!
To do this mod, you'll need...
a small Phillips screwdriver
sidecuts (wire cutters)
some electrical tape
a soldering iron
a package of 100K ohm 1/4 watt resistors from Radio Shack
(and of course, the Insten cradle.)
Step 1: Disassembly/Prep
With the feet removed, the four screws (that hold the case together) will be exposed. Remove them.
Pull off the bottom cover, flip it over and use it as a nice little tray for the screws so they don't get lost.
Cut a couple of small pieces of electrical tape and stick them (in two layers) right above the 4 solder points for the USB connector as shown in the picture. (That picture was taken after one of the resistors was already soldered in place. The one I took before soldering that resistor came out blurry, so I had to use this one.)
Step 2: Soldering
1. Bend a resistor so the legs are together, then cut the long leg so the legs are equal length.
2. Use a piece of electrical tape to tape the resistor in place so that the legs line up touching the 2 left solder points on the USB connector.
3. Only touching the tip of the soldering iron to the solder point on the circuit board (not the leg of the resistor - wouldn't want to move it!), feed a little solder in.
Use as little solder as possible. Big balls of solder will form solder bridges between the solder points on the circuit board, thus causing an unwanted short that may ruin the cradle and possibly even damage your iPhone. Be careful!
4. When both legs are soldered, remove the electrical tape holding the resistor in place. Be gentle and hold the resistor down while removing the tape. If either of the legs comes unsoldered during the tape removal, your connections weren't strong enough anyway, so resolder until it's right.
Repeat steps 1-4 to attach a second resistor across the two right solder points.
When finished, reassemble. You're done!