Assist stopped working in my 04 X5 and I had upgraded the TCU so I could have both bluetooth and assist. Dealer was giving me a hard time because the TCU I had "doesn't belong in my car". Long story short they opened a PUMA case and the new TCU (2 revisons from my P/N) is on backorder / limited availability and can only be ordered via BMW tech. Hopefully it will be here soon. I've already contacted BMW Assist to request to have the money I paid for the assist service for the last 8 month refunded (or applied to my account).
Not sure what is going on, but there seem to be a lot of X5s with Assist failing.
-Jeff