Bluetooth setup for my car. Can I use two different cell phones in my car? I have a bluetooth adapter from Mercedes. I have programmed my wife's cell phone to work with the car phone system. Can I add my cell phone to also work witht the car phone system?

If your Nissan Sentra does not come with Bluetooth built-in, you can still add it with an aftermarket Bluetooth receiver. These receivers can be found online or at electronics stores and are relatively inexpensive.
To install the receiver, you can follow these steps:

1. Turn off your car's ignition and open the glove box.
2. Locate the back of the car stereo and find the auxiliary input port. It should be a small, round port labeled "AUX."
3. Connect the Bluetooth receiver to the auxiliary input port with a 3.5mm auxiliary cable.
4. Connect the Bluetooth receiver to a power source, either through a USB port or a 12-volt adapter.
5. Turn on your car's ignition and switch the car stereo to auxiliary mode.
6. Turn on the Bluetooth receiver and pair it with your phone.
7. Once connected, you should be able to play music or take calls through your car stereo using the Bluetooth receiver.

Keep in mind that some aftermarket Bluetooth receivers may have slightly different installation instructions, so be sure to read the manual that comes with your specific receiver.

Differant model radio programs.

Turn iPhone Bluetooth On:First you want to make sure that Bluetooth is functioning on your iPhone. Click on the Settings icon from the iPhone desktop. From the settings screen click General to show the iPhone General Settings as displayed in the below image. Notice you can see if Bluetooth is on or off from this screen. General Settings screen you can click on Bluetooth to configure the Bluetooth settings. On the Bluetooth screen shown below click to the left of Off to turn Bluetooth On.

1. Begin Uconnect Setup:Now that Bluetooth is operational on the iPhone you can start the Uconnect process. Click the Uconnect button on the rear view mirror to begin. The voice from the Uconnect system will ask you to verbally select one of the options from the menu. Once Uconnect asks for your input say "Setup" to begin the process of syncing the iPhone.
2. Start Phone Pairing:Once you say setup in the above step the Uconnect system will list numerous options available from the setup menu. One of these options is "Phone Pairing" so when the Uconnect system asks for the choices from the setup menu say "Phone Pairing".
3. Pair a Phone:In the Phone Pairing menu you can modify current entries or begin pairing a new phone. After Uconnect lists all of the choices you should say "Pair a Phone" to begin the process of pairing the iPhone.
4. Uconnect Pin Code:The first step in pairing a phone is setting the Bluetooth Pin Code that authorizes that phone to pair with the Uconnect system. When asked for the Pin Code say any four digit combination such as "1 - 2 - 3 - 4". Uconnect will repeat back the Pin Code so you can verify it has recorded properly.
5. Connect iPhone To Uconnect:After you have set the Pin Code for the Uconnect system you need to view the iPhone's Bluetooth Settings screen which you can get to following the steps in Step 1 above. Before the Uconnect system shows up in Bluetooth the Bluetooth Settings screen will look similar to the below where you may have other Bluetooth devices showing or not.After a couple seconds the Uconnect system will display as "Hands Free" as shown in the below image. Notice it states that it is not yet paired,,,,,
6. Click on the Hands Free device showing in the Bluetooth devices list above. This will open a new screen as shown in the below image that prompts you for the Pin Code you specified in Step 5.
   
   Enter the Pin Code and then click the Connect button in the top right corner of the above window. This will pair the iPhone with Uconnect and take you back to the Bluetooth devices screen where the Uconnect Hands Free device will now show Connected as shown in the below image.
   
   After the device is connected you will be prompted by the Uconnect voice again so proceed to the below steps.
7. Phone Name & Priority: After connecting the iPhone you will then name the phone and set a priority between one and seven. Name the phone anything you would like and if this is your primary phone set the priority to one so this phone always connects at a higher priority than any other phone.
8. Verify & Test:Now have a friend dial your cell phone while you are in your car to see if the music volume lowers and the Uconnect voice tells you there is an incoming call from a certain number. To make calls you can press the Uconnect button and follow the voice prompts.
The Uconnect system is a great way to safely use your cell phone in the car.

Yes this is possible but the Bluetooth adapter must have compatible drivers loaded.....unlike computers you can't load a suitable driver! You will have to trial and error different makes and see if it works!

I know that 2004 BMWs used a Bluetooth protocol that is now obsolete. There are no longer any cell phones made that will pair with a 2004 BMW unless you get a very expensive upgrade to your Bluetooth module from BMW. Not worth it. When my wife got a new phone several years ago, she had to switch to aftermarket Bluetooth devices because as I recall, it was something like $2k to upgrade the Bluetooth in her '04 330i.
I was under the impression that 2005 BMWs use a more current Bluetooth communication protocol, but I don't know that for sure. If your car is an early 2005, I would suspect that perhaps it uses the same protocol as the '04s.

Go to the dealer and buy a bluetooth unit for your car fix it in to the phone cradle and same time ask them to activate the bluetooth in your car for you, service adviser will do it for you free, only service free you must have to pay for bluetooth unit,

"How do I use the phone"
-Read the cars/cell phones User Manual.

"do I have to buy a phone specific to c230"
-Probably not, as long as it has bluetooth.

any cellphone that has a bluetooth function works

try using the phone to locate the car. when pairing up.