A forum member has fitted a parrot CK3000 in an E46 Saloon HERE. It should give you a rough idea what it will entail and if paying £50 for fitting is worth it for you NOT to have to do it?
I'm sure you'll need a SOT lead, The SOT lead allows an easy connection between your radio and parrot kit - means you don't have to cut any
wires or work out what wires in the radio loom should connect to which wires on the parrot loom - it will then mute the radio when a call comes in and route the phone audio through the speakers.
There are SOT leads linked from this page, I'm not tipping this site but you'll be able to get the SOT code and shop around for the best price.HERE
Should you prefer to keep with the brand Parrot HERE is the Parrot Website with a drop down configuration table which will help you select the correct Parrot lead?