Can I use my Old car kit with my New Phone?

In Short. Not Likely.
The older car kits for most phones included a cradle that was specific to one brand and model combination of cell phone.
This is not how the game is played any longer.
Most new phones do not have a "car kit" specifically for them, unless they are a top end smart phones. (iPhone 4/ Blackberry/ Droid etc...)
For everyone else the New BLUETOOTH version 2.1 car kits are Bluetooth Enabled and are Awesome!
Bluetooth version 2.1 car kits are multi-point pairing, which means two phones can use the audio simultaneously! Not only are you NOT limited to using just one phone with the kit, but every time you upgrade the phone, as long as it has Bluetooth it works.
DSP with dual microphones will eliminate background noise very well.
ISO "Plug and Play" harnesses make installation quick, easy, and don't void warranties on your car or the car kit! Car kits also deliver the clearest audio possible through your car stereo speakers during a call, and resume music when the call is hung up. (If your phone supports A2DP Bluetooth profile, you can even stream your music from the cell phone to the stereo!)

We sell over 40 different car kits depending on the Bluetooth Profile of your phone.

So Is your old Car kit worth keeping....No.
Is it worth upgrading one last time..... I would say so.

For the BEST OEM "Plug and Play" car kit we suggest Scosche Blue Fusion Car Kits that allow steering wheel control and Stereo button controls for GM, Toyota, and Honda.

Then their is the Top of the line Bury CC9060IQ Touch screen and voice control that is so Awesome even the Government orders them and your Friends will want one too!

The CellProGuy