Works perfectly. I was able to retrofit a new GSM TCU (manufactured 05.2010) into my 2006 (04/05 build) E90 without any issues whatsoever.
ISTA/P picked up the new FZD and TCU and programmed them perfectly.
So if anyone was wondering if they wanted to buy a TCU unit, you can use either the GSM or the CDMA version, at least in the older models. Although, I'm pretty sure you can use any version you want and it'll work just fine.