Simple Hands free car phone

- I want to have a simple hands free car phone for my car. I do know that many ready made kits are available but where i live they are not easily available and even if,the cost will be exorbitant.
- Keeping the prevaling regulations of not to use mobile phone during car driving, I feel Bluetooth hands free set would be the most feasible. My requirement is to respond only to the incoming calls only. My thinking goes this way:

a) Pick a Bluetooth headset and disconnect the mike and earphone connections.
b) Connect earphone ends to an amplifier + speaker.
c) Mike inputs connections of Bluetooth device connected to an amplifier with good pick up mike.
d) Amplifier will be placed separately and powered by +12 V DC.( cigarette lighter interface)
e) Mike will be fixed on the Dash board and as closer to the steering wheel.

Idea may look crude, but one has to start somewhere to grow in learning. Could somebody give some more info to go about?

Thanks in advance.

You will have acoustical feedback howling.

When you speak into a phone, you hear yourself. The phone is made to give "sidetone" which is your own voice so you can hear how loud you are talking, and it covers up the echoe produced on the 4-wire to 2-wire hybrid converters.
When the speaker in your car produces a sound then the mic hears it and the amplified sound is produced in the speaker as sidetone and the sound goes around and around making feedback howling.

You need a speakerphone circuit to switch the speaker and mic. Modern speakerphones use a DSP echo canceller to cancel the feedback.