Does anyone know if I can retrofit the wireless phone box to my 2016 facelift A3 S line?

Hi Mark, 

I would imagine no it can be retrofitting but I don't think it'll be cheap. I believe the phone box came with the tech pack. Here is a link to another thread on here that responded too. It may be useful. 

There's also this company I follow on Facebook which may be worth contacting. There work looks pretty good but can't say I've had any first hand experience of their work.

https://www.facebook.com/Lightrofit/

Hope I've helped :) 

Cheers

Steve

Many thanks Steve, I will look into the facebook company. 

Not a problem Mark. Glad I could help :)