ychap

i have a 2004 545i and want to know what are my options to play music through my phone

Boost7

All depends on how much you willing to spend just to get sounds from your phone to the car.

I went with the aux input and used a headphone jack. Not the most latest and greatest high tech, but gets the job done.

I'm sure others will chime in on what they did, but I'm sure they paid a lot more also.

ychap

what do i all need to install aux imput

edsub

Get / make an aux connector, plug it into the back of the head unit, have it activated and youre done (theoretically, have to do mine still).

Once you have that adding Bluetooth is easy as well: Buy a cheap Bluetooth A2DP module, power it via a 12V to USB converter (you can use the power of the accessory power connector on the left side of the glove compartment, where the torch is/used to be) and connect it to your new AUX-in.
The you only need to pair with the BT module in order to be able to stream via BT.

ychap

How do i activate it?? Do I take to the dealership I asked if they can code they said no I don't know wht mean. Would it be easier to it myself wht would I all need and where can I buy it