Going from the old style key fob to the new style B7 fob is a nice relatively cheap and easy upgrade.
There are two options to source a B7 FOB.
Used OEM B7 keys go for as low as 23 bucks on ebay. New Chinese knock offs go for 20 bucks on ebay. Some are 3 dollars, but thats only a case without a circuit board.
The ebay ones are cheeeeeaaaaaaappppp. The battery cover tabs break easily, the coating scratches easy and the button material feels even cheaper and wear quickly. Snag an OEM unit if you can.
Also some ebay units do not come with a panic button, which in someways looks cleaner.
Other than quality, the main difference is the ebay ones require reprogramming every time you disconnect the car battery or replace the fob batteries. OEM stay programmed forever(where you only need to hold the lock button and insert into ignition/ON and its re-programmed, the ebays ones its a longer process).
The used OEM will need a new blank key blade. Where the ebay ones will come with a blank already. The ebay ones do NOT come with a ID48 chip. So source accordingly.
There are essentially two functions to the FOB. The first is to turn the car on. The second function is the lock/unlock/trunk/panic buttons. These two functions are completely independent from one another from a hardware and programming standpoint.
To get the proper lock/unlock/trunk/panic buttons to work, you need a key with an FCC ID : MYT 4073A
8E0 837 220 L or R
All of this information is just behind where the blade rests, so no need to disassemble anything to locate.
To get the turning of the car on to function properly, you need a virgin IMMO ID48 chip, or steal your old B6 chip. Your old B6 chip is the ONLY thing that can be pillaged from the old remote. Well and the battery, but thats it. Not the blade or circuit board.
Virgin IMMO Chips can be had here:
or on ebay. I've sourced from both with successful results.
ID48 chip required
Both Ebay and OEM will need new blades to be cut. From the stories I've read online(I'm paraphrasing here), IF the dealership is willing to touch your blade, they send it off to a desert in Europe, apparently to a skilled basket weaver that lives in a house for fun, who then ships it to an unknown PO box in Belarus to be inspected by a troll, who rolls a deltoidal icositetrahedron, that determines if the fathers will grant permission of such witch craft to take place. If so, he'll wrap the forged metal in a black magic carpet back to Germany, which actually acts as a time machine to when the merger of the four companies originally took place in 1910 to form Audi. to then be cut by some young engineering student for 190 bucks, which is cheap given the process it goes through. But seriously, I dont think dealers cut blades.
Or you can goto your local lock smith, call first, and they can do it for 15-20 bucks.
You will also need the latest CCCM to get the B7 fob to work, covered in the sections below.