Your right, Telstra's NextG is UMTS 850 with fallback to 900/1800 GSM

Sorry it wont work on NextG but it will operate with the NextG sim on 900/1800 2G GSM band.

So if your not worried about using NextG data/internet services you will be fine, it will work for phone calls no problem. Just use Wifi for data at home and office ect..

Telstra way overcharge for NextG data anyway.

Regards
Andrew